rq->clock{,_task} are serialized by rq->lock, verify this.

One immediate fail is the usage in scale_rt_capability, so 'annotate'
that for now, there's more 'funny' there. Maybe change rq->lock into a
raw_seqlock_t?

(Only 32-bit is affected)
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150105103554.361872747@infradead.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: umgwanakikbuti@gmail.com
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Child has the same decay_count as parent. If it's not zero,
we add it to parent's cfs_rq->removed_load:

wake_up_new_task()->set_task_cpu()->migrate_task_rq_fair().

Child's load is a just garbade after copying of parent,
it hasn't been on cfs_rq yet, and it must not be added to
cfs_rq::removed_load in migrate_task_rq_fair().

The patch moves sched_entity::avg::decay_count intialization
in sched_fork(). So, migrate_task_rq_fair() does not change
removed_load.
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NBen Segall <bsegall@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1418644618.6074.13.camel@tkhaiSigned-off-by: NIngo Molnar <mingo@kernel.org>

In __synchronize_entity_decay(), if "decays" happens to be zero,
se->avg.decay_count will not be zeroed, holding the positive value
assigned when dequeued last time.

This is problematic in the following case:
If this runnable task is CFS-balanced to other CPUs soon afterwards,
migrate_task_rq_fair() will treat it as a blocked task due to its
non-zero decay_count, thereby adding its load to cfs_rq->removed_load
wrongly.

Thus, we must zero se->avg.decay_count in this case as well.
Signed-off-by: NXunlei Pang <pang.xunlei@linaro.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NBen Segall <bsegall@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1418745509-2609-1-git-send-email-pang.xunlei@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

When alloc_fair_sched_group() in sched_create_group() fails,
free_sched_group() is called, and free_fair_sched_group() is called by
free_sched_group(). Since destroy_cfs_bandwidth() is called by
free_fair_sched_group() without calling init_cfs_bandwidth(),
RCU stall occurs at hrtimer_cancel():

  INFO: rcu_sched self-detected stall on CPU { 1}  (t=60000 jiffies g=13074 c=13073 q=0)
  Task dump for CPU 1:
  (fprintd)       R  running task        0  6249      1 0x00000088
  ...
  Call Trace:
   <IRQ>  [<ffffffff81094988>] sched_show_task+0xa8/0x110
   [<ffffffff81097acd>] dump_cpu_task+0x3d/0x50
   [<ffffffff810c3a80>] rcu_dump_cpu_stacks+0x90/0xd0
   [<ffffffff810c7751>] rcu_check_callbacks+0x491/0x700
   [<ffffffff810cbf2b>] update_process_times+0x4b/0x80
   [<ffffffff810db046>] tick_sched_handle.isra.20+0x36/0x50
   [<ffffffff810db0a2>] tick_sched_timer+0x42/0x70
   [<ffffffff810ccb19>] __run_hrtimer+0x69/0x1a0
   [<ffffffff810db060>] ? tick_sched_handle.isra.20+0x50/0x50
   [<ffffffff810ccedf>] hrtimer_interrupt+0xef/0x230
   [<ffffffff810452cb>] local_apic_timer_interrupt+0x3b/0x70
   [<ffffffff8164a465>] smp_apic_timer_interrupt+0x45/0x60
   [<ffffffff816485bd>] apic_timer_interrupt+0x6d/0x80
   <EOI>  [<ffffffff810cc588>] ? lock_hrtimer_base.isra.23+0x18/0x50
   [<ffffffff81193cf1>] ? __kmalloc+0x211/0x230
   [<ffffffff810cc9d2>] hrtimer_try_to_cancel+0x22/0xd0
   [<ffffffff81193cf1>] ? __kmalloc+0x211/0x230
   [<ffffffff810ccaa2>] hrtimer_cancel+0x22/0x30
   [<ffffffff810a3cb5>] free_fair_sched_group+0x25/0xd0
   [<ffffffff8108df46>] free_sched_group+0x16/0x40
   [<ffffffff810971bb>] sched_create_group+0x4b/0x80
   [<ffffffff810aa383>] sched_autogroup_create_attach+0x43/0x1c0
   [<ffffffff8107dc9c>] sys_setsid+0x7c/0x110
   [<ffffffff81647729>] system_call_fastpath+0x12/0x17

Check whether init_cfs_bandwidth() was called before calling
destroy_cfs_bandwidth().
Signed-off-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
[ Move the check into destroy_cfs_bandwidth() to aid compilability. ]
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/201412252210.GCC30204.SOMVFFOtQJFLOH@I-love.SAKURA.ne.jpSigned-off-by: NIngo Molnar <mingo@kernel.org>

In effective_load, we have (long w * unsigned long tg->shares) / long W,
when w is negative, it is cast to unsigned long and hence the product is
insanely large. Fix this by casting tg->shares to long.
Reported-by: NSasha Levin <sasha.levin@oracle.com>
Signed-off-by: NYuyang Du <yuyang.du@intel.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dave Jones <davej@redhat.com>
Cc: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20141219002956.GA25405@intel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Commit caeb178c ("sched/fair: Make update_sd_pick_busiest() return
'true' on a busier sd") changes groups to be ranked in the order of
overloaded > imbalance > other, and busiest group is picked according
to this order.

sgs->group_capacity_factor is used to check if the group is overloaded.

When the child domain prefers tasks to go to siblings first, the
sgs->group_capacity_factor will be set lower than one in order to
move all the excess tasks away.

However, group overloaded status is not updated when
sgs->group_capacity_factor is set to lower than one, which leads to us
missing to find the busiest group.

This patch fixes it by updating group overloaded status when sg capacity
factor is set to one, in order to find the busiest group accurately.
Signed-off-by: NWanpeng Li <wanpeng.li@linux.intel.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Kirill Tkhai <ktkhai@parallels.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1415144690-25196-1-git-send-email-wanpeng.li@linux.intel.com
[ Fixed the changelog. ]
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Move the p->nr_cpus_allowed check into kernel/sched/core.c: select_task_rq().
This change will make fair.c, rt.c, and deadline.c all start with the
same logic.
Suggested-and-Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NWanpeng Li <wanpeng.li@linux.intel.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: "pang.xunlei" <pang.xunlei@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1415150077-59053-1-git-send-email-wanpeng.li@linux.intel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Nobody iterates over numa_group::task_list, this just confuses the readers.
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1415358456.28592.17.camel@tkhaiSigned-off-by: NIngo Molnar <mingo@kernel.org>

Commit d670ec13 "posix-cpu-timers: Cure SMP wobbles" fixes one glibc
test case in cost of breaking another one. After that commit, calling
clock_nanosleep(TIMER_ABSTIME, X) and then clock_gettime(&Y) can result
of Y time being smaller than X time.

Reproducer/tester can be found further below, it can be compiled and ran by:

	gcc -o tst-cpuclock2 tst-cpuclock2.c -pthread
	while ./tst-cpuclock2 ; do : ; done

This reproducer, when running on a buggy kernel, will complain
about "clock_gettime difference too small".

Issue happens because on start in thread_group_cputimer() we initialize
sum_exec_runtime of cputimer with threads runtime not yet accounted and
then add the threads runtime to running cputimer again on scheduler
tick, making it's sum_exec_runtime bigger than actual threads runtime.

KOSAKI Motohiro posted a fix for this problem, but that patch was never
applied: https://lkml.org/lkml/2013/5/26/191 .

This patch takes different approach to cure the problem. It calls
update_curr() when cputimer starts, that assure we will have updated
stats of running threads and on the next schedule tick we will account
only the runtime that elapsed from cputimer start. That also assure we
have consistent state between cpu times of individual threads and cpu
time of the process consisted by those threads.

Full reproducer (tst-cpuclock2.c):

	#define _GNU_SOURCE
	#include <unistd.h>
	#include <sys/syscall.h>
	#include <stdio.h>
	#include <time.h>
	#include <pthread.h>
	#include <stdint.h>
	#include <inttypes.h>

	/* Parameters for the Linux kernel ABI for CPU clocks.  */
	#define CPUCLOCK_SCHED          2
	#define MAKE_PROCESS_CPUCLOCK(pid, clock) \
		((~(clockid_t) (pid) << 3) | (clockid_t) (clock))

	static pthread_barrier_t barrier;

	/* Help advance the clock.  */
	static void *chew_cpu(void *arg)
	{
		pthread_barrier_wait(&barrier);
		while (1) ;

		return NULL;
	}

	/* Don't use the glibc wrapper.  */
	static int do_nanosleep(int flags, const struct timespec *req)
	{
		clockid_t clock_id = MAKE_PROCESS_CPUCLOCK(0, CPUCLOCK_SCHED);

		return syscall(SYS_clock_nanosleep, clock_id, flags, req, NULL);
	}

	static int64_t tsdiff(const struct timespec *before, const struct timespec *after)
	{
		int64_t before_i = before->tv_sec * 1000000000ULL + before->tv_nsec;
		int64_t after_i = after->tv_sec * 1000000000ULL + after->tv_nsec;

		return after_i - before_i;
	}

	int main(void)
	{
		int result = 0;
		pthread_t th;

		pthread_barrier_init(&barrier, NULL, 2);

		if (pthread_create(&th, NULL, chew_cpu, NULL) != 0) {
			perror("pthread_create");
			return 1;
		}

		pthread_barrier_wait(&barrier);

		/* The test.  */
		struct timespec before, after, sleeptimeabs;
		int64_t sleepdiff, diffabs;
		const struct timespec sleeptime = {.tv_sec = 0,.tv_nsec = 100000000 };

		/* The relative nanosleep.  Not sure why this is needed, but its presence
		   seems to make it easier to reproduce the problem.  */
		if (do_nanosleep(0, &sleeptime) != 0) {
			perror("clock_nanosleep");
			return 1;
		}

		/* Get the current time.  */
		if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &before) < 0) {
			perror("clock_gettime[2]");
			return 1;
		}

		/* Compute the absolute sleep time based on the current time.  */
		uint64_t nsec = before.tv_nsec + sleeptime.tv_nsec;
		sleeptimeabs.tv_sec = before.tv_sec + nsec / 1000000000;
		sleeptimeabs.tv_nsec = nsec % 1000000000;

		/* Sleep for the computed time.  */
		if (do_nanosleep(TIMER_ABSTIME, &sleeptimeabs) != 0) {
			perror("absolute clock_nanosleep");
			return 1;
		}

		/* Get the time after the sleep.  */
		if (clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &after) < 0) {
			perror("clock_gettime[3]");
			return 1;
		}

		/* The time after sleep should always be equal to or after the absolute sleep
		   time passed to clock_nanosleep.  */
		sleepdiff = tsdiff(&sleeptimeabs, &after);
		if (sleepdiff < 0) {
			printf("absolute clock_nanosleep woke too early: %" PRId64 "\n", sleepdiff);
			result = 1;

			printf("Before %llu.%09llu\n", before.tv_sec, before.tv_nsec);
			printf("After  %llu.%09llu\n", after.tv_sec, after.tv_nsec);
			printf("Sleep  %llu.%09llu\n", sleeptimeabs.tv_sec, sleeptimeabs.tv_nsec);
		}

		/* The difference between the timestamps taken before and after the
		   clock_nanosleep call should be equal to or more than the duration of the
		   sleep.  */
		diffabs = tsdiff(&before, &after);
		if (diffabs < sleeptime.tv_nsec) {
			printf("clock_gettime difference too small: %" PRId64 "\n", diffabs);
			result = 1;
		}

		pthread_cancel(th);

		return result;
	}
Signed-off-by: NStanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20141112155843.GA24803@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Because the whole numa task selection stuff runs with preemption
enabled (its long and expensive) we can end up migrating and selecting
oneself as a swap target. This doesn't really work out well -- we end
up trying to acquire the same lock twice for the swap migrate -- so
avoid this.
Reported-and-Tested-by: NSasha Levin <sasha.levin@oracle.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20141110100328.GF29390@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

This patch simplifies task_struct by removing the four numa_* pointers
in the same array and replacing them with the array pointer. By doing this,
on x86_64, the size of task_struct is reduced by 3 ulong pointers (24 bytes on
x86_64).

A new parameter is added to the task_faults_idx function so that it can return
an index to the correct offset, corresponding with the old precalculated
pointers.

All of the code in sched/ that depended on task_faults_idx and numa_* was
changed in order to match the new logic.
Signed-off-by: NIulia Manda <iulia.manda21@gmail.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: mgorman@suse.de
Cc: dave@stgolabs.net
Cc: riel@redhat.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20141031001331.GA30662@winterfellSigned-off-by: NIngo Molnar <mingo@kernel.org>

Idle cpu is idler than non-idle cpu, so we needn't search for least_loaded_cpu
after we have found an idle cpu.
Signed-off-by: NYao Dongdong <yaodongdong@huawei.com>
Reviewed-by: NSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1414469286-6023-1-git-send-email-yaodongdong@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

In pseudo-interleaved numa_groups, all tasks try to relocate to
the group's preferred_nid.  When a group is spread across multiple
NUMA nodes, this can lead to tasks swapping their location with
other tasks inside the same group, instead of swapping location with
tasks from other NUMA groups. This can keep NUMA groups from converging.

Examining all nodes, when dealing with a task in a pseudo-interleaved
NUMA group, avoids this problem. Note that only CPUs in nodes that
improve the task or group score are examined, so the loop isn't too
bad.
Tested-by: NVinod Chegu <chegu_vinod@hp.com>
Signed-off-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: "Vinod Chegu" <chegu_vinod@hp.com>
Cc: mgorman@suse.de
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20141009172747.0d97c38c@annuminas.surriel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

On systems with complex NUMA topologies, the node scoring is adjusted
to allow workloads to converge on nodes that are near each other.

The way a task group's preferred nid is determined needs to be adjusted,
in order for the preferred_nid to be consistent with group_weight scoring.
This ensures that we actually try to converge workloads on adjacent nodes.
Signed-off-by: NRik van Riel <riel@redhat.com>
Tested-by: NChegu Vinod <chegu_vinod@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: mgorman@suse.de
Cc: chegu_vinod@hp.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1413530994-9732-6-git-send-email-riel@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

In order to do task placement on systems with complex NUMA topologies,
it is necessary to count the faults on nodes nearby the node that is
being examined for a potential move.

In case of a system with a backplane interconnect, we are dealing with
groups of NUMA nodes; each of the nodes within a group is the same number
of hops away from nodes in other groups in the system. Optimal placement
on this topology is achieved by counting all nearby nodes equally. When
comparing nodes A and B at distance N, nearby nodes are those at distances
smaller than N from nodes A or B.

Placement strategy on a system with a glueless mesh NUMA topology needs
to be different, because there are no natural groups of nodes determined
by the hardware. Instead, when dealing with two nodes A and B at distance
N, N >= 2, there will be intermediate nodes at distance < N from both nodes
A and B. Good placement can be achieved by right shifting the faults on
nearby nodes by the number of hops from the node being scored. In this
context, a nearby node is any node less than the maximum distance in the
system away from the node. Those nodes are skipped for efficiency reasons,
there is no real policy reason to do so.

Placement policy on directly connected NUMA systems is not affected.
Signed-off-by: NRik van Riel <riel@redhat.com>
Tested-by: NChegu Vinod <chegu_vinod@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: mgorman@suse.de
Cc: chegu_vinod@hp.com
Link: http://lkml.kernel.org/r/1413530994-9732-5-git-send-email-riel@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Preparatory patch for adding NUMA placement on systems with
complex NUMA topology. Also fix a potential divide by zero
in group_weight()
Signed-off-by: NRik van Riel <riel@redhat.com>
Tested-by: NChegu Vinod <chegu_vinod@hp.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: mgorman@suse.de
Cc: chegu_vinod@hp.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1413530994-9732-4-git-send-email-riel@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

File /proc/sys/kernel/numa_balancing_scan_size_mb allows writing of zero.

This bash command reproduces problem:

$ while :; do echo 0 > /proc/sys/kernel/numa_balancing_scan_size_mb; \
	   echo 256 > /proc/sys/kernel/numa_balancing_scan_size_mb; done

	divide error: 0000 [#1] SMP
	Modules linked in:
	CPU: 0 PID: 24112 Comm: bash Not tainted 3.17.0+ #8
	Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
	task: ffff88013c852600 ti: ffff880037a68000 task.ti: ffff880037a68000
	RIP: 0010:[<ffffffff81074191>]  [<ffffffff81074191>] task_scan_min+0x21/0x50
	RSP: 0000:ffff880037a6bce0  EFLAGS: 00010246
	RAX: 0000000000000a00 RBX: 00000000000003e8 RCX: 0000000000000000
	RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88013c852600
	RBP: ffff880037a6bcf0 R08: 0000000000000001 R09: 0000000000015c90
	R10: ffff880239bf6c00 R11: 0000000000000016 R12: 0000000000003fff
	R13: ffff88013c852600 R14: ffffea0008d1b000 R15: 0000000000000003
	FS:  00007f12bb048700(0000) GS:ffff88007da00000(0000) knlGS:0000000000000000
	CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
	CR2: 0000000001505678 CR3: 0000000234770000 CR4: 00000000000006f0
	Stack:
	 ffff88013c852600 0000000000003fff ffff880037a6bd18 ffffffff810741d1
	 ffff88013c852600 0000000000003fff 000000000002bfff ffff880037a6bda8
	 ffffffff81077ef7 ffffea0008a56d40 0000000000000001 0000000000000001
	Call Trace:
	 [<ffffffff810741d1>] task_scan_max+0x11/0x40
	 [<ffffffff81077ef7>] task_numa_fault+0x1f7/0xae0
	 [<ffffffff8115a896>] ? migrate_misplaced_page+0x276/0x300
	 [<ffffffff81134a4d>] handle_mm_fault+0x62d/0xba0
	 [<ffffffff8103e2f1>] __do_page_fault+0x191/0x510
	 [<ffffffff81030122>] ? native_smp_send_reschedule+0x42/0x60
	 [<ffffffff8106dc00>] ? check_preempt_curr+0x80/0xa0
	 [<ffffffff8107092c>] ? wake_up_new_task+0x11c/0x1a0
	 [<ffffffff8104887d>] ? do_fork+0x14d/0x340
	 [<ffffffff811799bb>] ? get_unused_fd_flags+0x2b/0x30
	 [<ffffffff811799df>] ? __fd_install+0x1f/0x60
	 [<ffffffff8103e67c>] do_page_fault+0xc/0x10
	 [<ffffffff8150d322>] page_fault+0x22/0x30
	RIP  [<ffffffff81074191>] task_scan_min+0x21/0x50
	RSP <ffff880037a6bce0>
	---[ end trace 9a826d16936c04de ]---

Also fix race in task_scan_min (it depends on compiler behaviour).
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dario Faggioli <raistlin@linux.it>
Cc: David Rientjes <rientjes@google.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Link: http://lkml.kernel.org/r/1413455977.24793.78.camel@tkhaiSigned-off-by: NIngo Molnar <mingo@kernel.org>

While offling node by hot removing memory, the following divide error
occurs:

  divide error: 0000 [#1] SMP
  [...]
  Call Trace:
   [...] handle_mm_fault
   [...] ? try_to_wake_up
   [...] ? wake_up_state
   [...] __do_page_fault
   [...] ? do_futex
   [...] ? put_prev_entity
   [...] ? __switch_to
   [...] do_page_fault
   [...] page_fault
  [...]
  RIP  [<ffffffff810a7081>] task_numa_fault
   RSP <ffff88084eb2bcb0>

The issue occurs as follows:
  1. When page fault occurs and page is allocated from node 1,
     task_struct->numa_faults_buffer_memory[] of node 1 is
     incremented and p->numa_faults_locality[] is also incremented
     as follows:

     o numa_faults_buffer_memory[]       o numa_faults_locality[]
              NR_NUMA_HINT_FAULT_TYPES
             |      0     |     1     |
     ----------------------------------  ----------------------
      node 0 |      0     |     0     |   remote |      0     |
      node 1 |      0     |     1     |   locale |      1     |
     ----------------------------------  ----------------------

  2. node 1 is offlined by hot removing memory.

  3. When page fault occurs, fault_types[] is calculated by using
     p->numa_faults_buffer_memory[] of all online nodes in
     task_numa_placement(). But node 1 was offline by step 2. So
     the fault_types[] is calculated by using only
     p->numa_faults_buffer_memory[] of node 0. So both of fault_types[]
     are set to 0.

  4. The values(0) of fault_types[] pass to update_task_scan_period().

  5. numa_faults_locality[1] is set to 1. So the following division is
     calculated.

        static void update_task_scan_period(struct task_struct *p,
                                unsigned long shared, unsigned long private){
        ...
                ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared));
        }

  6. But both of private and shared are set to 0. So divide error
     occurs here.

The divide error is rare case because the trigger is node offline.
This patch always increments denominator for avoiding divide error.
Signed-off-by: NYasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/54475703.8000505@jp.fujitsu.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Unlocked access to dst_rq->curr in task_numa_compare() is racy.
If curr task is exiting this may be a reason of use-after-free:

task_numa_compare()                    do_exit()
    ...                                        current->flags |= PF_EXITING;
    ...                                    release_task()
    ...                                        ~~delayed_put_task_struct()~~
    ...                                    schedule()
    rcu_read_lock()                        ...
    cur = ACCESS_ONCE(dst_rq->curr)        ...
        ...                                rq->curr = next;
        ...                                    context_switch()
        ...                                        finish_task_switch()
        ...                                            put_task_struct()
        ...                                                __put_task_struct()
        ...                                                    free_task_struct()
        task_numa_assign()                                     ...
            get_task_struct()                                  ...

As noted by Oleg:

  <<The lockless get_task_struct(tsk) is only safe if tsk == current
    and didn't pass exit_notify(), or if this tsk was found on a rcu
    protected list (say, for_each_process() or find_task_by_vpid()).
    IOW, it is only safe if release_task() was not called before we
    take rcu_read_lock(), in this case we can rely on the fact that
    delayed_put_pid() can not drop the (potentially) last reference
    until rcu_read_unlock().

    And as Kirill pointed out task_numa_compare()->task_numa_assign()
    path does get_task_struct(dst_rq->curr) and this is not safe. The
    task_struct itself can't go away, but rcu_read_lock() can't save
    us from the final put_task_struct() in finish_task_switch(); this
    reference goes away without rcu gp>>

The patch provides simple check of PF_EXITING flag. If it's not set,
this guarantees that call_rcu() of delayed_put_task_struct() callback
hasn't happened yet, so we can safely do get_task_struct() in
task_numa_assign().

Locked dst_rq->lock protects from concurrency with the last schedule().
Reusing or unmapping of cur's memory may happen without it.
Suggested-by: NOleg Nesterov <oleg@redhat.com>
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1413962231.19914.130.camel@tkhaiSigned-off-by: NIngo Molnar <mingo@kernel.org>

1. vma_policy_mof(task) is simply not safe unless task == current,
   it can race with do_exit()->mpol_put(). Remove this arg and update
   its single caller.

2. vma can not be NULL, remove this check and simplify the code.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We already reschedule env.dst_cpu in attach_tasks()->check_preempt_curr()
if this is necessary.

Furthermore, a higher priority class task may be current on dest rq,
we shouldn't disturb it.
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Cc: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140930210441.5258.55054.stgit@localhostSigned-off-by: NIngo Molnar <mingo@kernel.org>

Since commit caeb178c ("sched/fair: Make update_sd_pick_busiest() ...")
sd_pick_busiest returns a group that can be neither imbalanced nor overloaded
but is only more loaded than others. This change has been introduced to ensure
a better load balance in system that are not overloaded but as a side effect,
it can also generate useless active migration between groups.

Let take the example of 3 tasks on a quad cores system. We will always have an
idle core so the load balance will find a busiest group (core) whenever an ILB
is triggered and it will force an active migration (once above
nr_balance_failed threshold) so the idle core becomes busy but another core
will become idle. With the next ILB, the freshly idle core will try to pull the
task of a busy CPU.
The number of spurious active migration is not so huge in quad core system
because the ILB is not triggered so much. But it becomes significant as soon as
you have more than one sched_domain level like on a dual cluster of quad cores
where the ILB is triggered every tick when you have more than 1 busy_cpu

We need to ensure that the migration generate a real improveùent and will not
only move the avg_load imbalance on another CPU.

Before caeb178c, the filtering of such use
case was ensured by the following test in f_b_g:

  if ((local->idle_cpus < busiest->idle_cpus) &&
		    busiest->sum_nr_running  <= busiest->group_weight)

This patch modified the condition to take into account situation where busiest
group is not overloaded: If the diff between the number of idle cpus in 2
groups is less than or equal to 1 and the busiest group is not overloaded,
moving a task will not improve the load balance but just move it.

A test with sysbench on a dual clusters of quad cores gives the following
results:

  command: sysbench --test=cpu --num-threads=5 --max-time=5 run

The HZ is 200 which means that 1000 ticks has fired during the test.

With Mainline, perf gives the following figures:

 Samples: 727  of event 'sched:sched_migrate_task'
 Event count (approx.): 727
  Overhead  Command          Shared Object  Symbol
  ........  ...............  .............  ..............
    12.52%  migration/1      [unknown]      [.] 00000000
    12.52%  migration/5      [unknown]      [.] 00000000
    12.52%  migration/7      [unknown]      [.] 00000000
    12.10%  migration/6      [unknown]      [.] 00000000
    11.83%  migration/0      [unknown]      [.] 00000000
    11.83%  migration/3      [unknown]      [.] 00000000
    11.14%  migration/4      [unknown]      [.] 00000000
    10.87%  migration/2      [unknown]      [.] 00000000
     2.75%  sysbench         [unknown]      [.] 00000000
     0.83%  swapper          [unknown]      [.] 00000000
     0.55%  ktps65090charge  [unknown]      [.] 00000000
     0.41%  mmcqd/1          [unknown]      [.] 00000000
     0.14%  perf             [unknown]      [.] 00000000

With this patch, perf gives the following figures

 Samples: 20  of event 'sched:sched_migrate_task'
 Event count (approx.): 20
  Overhead  Command          Shared Object  Symbol
  ........  ...............  .............  ..............
    80.00%  sysbench         [unknown]      [.] 00000000
    10.00%  swapper          [unknown]      [.] 00000000
     5.00%  ktps65090charge  [unknown]      [.] 00000000
     5.00%  migration/1      [unknown]      [.] 00000000
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1412170735-5356-1-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Combine two branches which do the same.
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140922183612.11015.64200.stgit@localhostSigned-off-by: NIngo Molnar <mingo@kernel.org>

The code in find_idlest_cpu() looks for the CPU with the smallest load.
However, if multiple CPUs are idle, the first idle CPU is selected
irrespective of the depth of its idle state.

Among the idle CPUs we should pick the one with with the shallowest idle
state, or the latest to have gone idle if all idle CPUs are in the same
state.  The later applies even when cpuidle is configured out.

This patch doesn't cover the following issues:

- The idle exit latency of a CPU might be larger than the time needed
  to migrate the waking task to an already running CPU with sufficient
  capacity, and therefore performance would benefit from task packing
  in such case (in most cases task packing is about power saving).

- Some idle states have a non negligible and non abortable entry latency
  which needs to run to completion before the exit latency can start.
  A concurrent patch series is making this info available to the cpuidle
  core.  Once available, the entry latency with the idle timestamp could
  determine when the exit latency may be effective.

Those issues will be handled in due course.  In the mean time, what
is implemented here should improve things already compared to the current
state of affairs.

Based on an initial patch from Daniel Lezcano.
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-pm@vger.kernel.org
Cc: linaro-kernel@lists.linaro.org
Link: http://lkml.kernel.org/n/tip-@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

current->state == TASK_DEAD means that the task is doing its
last schedule(), page fault is obviously impossible at this
stage.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Acked-by: NMel Gorman <mgorman@suse.de>
Acked-by: NRik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140921194743.GA30114@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Signed-off-by: NZhihui Zhang <zzhsuny@gmail.com>
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/1411262676-19928-1-git-send-email-zzhsuny@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Currently the task always wakes affine on this_cpu if the latter is idle.
Before waking up the task on this_cpu, we check that this_cpu capacity is not
significantly reduced because of RT tasks or irq activity.

Use case where the number of irq and/or the time spent under irq is important
will take benefit of this because the task that is woken up by irq or softirq
will not use the same CPU than irq (and softirq) but a idle one.
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-8-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

'capacity_orig' is only changed for systems with an SMT sched_domain level in order
to reflect the lower capacity of CPUs. Heterogenous systems also have to reflect an
original capacity that is different from the default value.

Create a more generic function arch_scale_cpu_capacity that can be also used by
non SMT platforms to set capacity_orig.

The __weak implementation of arch_scale_cpu_capacity() is the previous SMT variant,
in order to keep backward compatibility with the use of capacity_orig.

arch_scale_smt_capacity() and default_scale_smt_capacity() have been removed as
they were not used elsewhere than in arch_scale_cpu_capacity().
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: NKamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Reviewed-by: NPreeti U. Murthy <preeti@linux.vnet.ibm.com>
[ Added default_scale_cpu_capacity() back. ]
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-5-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The computation of avg_load and avg_load_per_task should only take into
account the number of CFS tasks. The non-CFS tasks are already taken into
account by decreasing the CPU's capacity and they will be tracked in the
CPU's utilization (group_utilization) of the next patches.
Reviewed-by: NPreeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-4-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

In wake_affine() I have tried to understand the meaning of the condition:

 (this_load <= load &&
  this_load + target_load(prev_cpu, idx) <= tl_per_task)

but I failed to find a use case that can take advantage of it and I haven't
found clear description in the previous commit's log.

Futhermore, the comment of the condition refers to the task_hot function that
was used before being replaced by the current condition:

/*
 * This domain has SD_WAKE_AFFINE and
 * p is cache cold in this domain, and
 * there is no bad imbalance.
 */

If we look more deeply the below condition:

 this_load + target_load(prev_cpu, idx) <= tl_per_task

When sync is clear, we have:

 tl_per_task = runnable_load_avg / nr_running
 this_load = max(runnable_load_avg, cpuload[idx])
 target_load =  max(runnable_load_avg', cpuload'[idx])

It implies that runnable_load_avg == 0 and nr_running <= 1 in order to match the
condition. This implies that runnable_load_avg == 0 too because of the
condition: this_load <= load.

but if this _load is null, 'balanced' is already set and the test is redundant.

If sync is set, it's not as straight forward as above (especially if cgroup
are involved) but the policy should be similar as we have removed a task that's
going to sleep in order to get a more accurate load and this_load values.

The current conclusion is that these additional condition don't give any benefit
so we can remove them.
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-3-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The imbalance flag can stay set whereas there is no imbalance.

Let assume that we have 3 tasks that run on a dual cores /dual cluster system.
We will have some idle load balance which are triggered during tick.
Unfortunately, the tick is also used to queue background work so we can reach
the situation where short work has been queued on a CPU which already runs a
task. The load balance will detect this imbalance (2 tasks on 1 CPU and an idle
CPU) and will try to pull the waiting task on the idle CPU. The waiting task is
a worker thread that is pinned on a CPU so an imbalance due to pinned task is
detected and the imbalance flag is set.

Then, we will not be able to clear the flag because we have at most 1 task on
each CPU but the imbalance flag will trig to useless active load balance
between the idle CPU and the busy CPU.

We need to reset of the imbalance flag as soon as we have reached a balanced
state. If all tasks are pinned, we don't consider that as a balanced state and
let the imbalance flag set.
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: NPreeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: riel@redhat.com
Cc: Morten.Rasmussen@arm.com
Cc: efault@gmx.de
Cc: nicolas.pitre@linaro.org
Cc: daniel.lezcano@linaro.org
Cc: dietmar.eggemann@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409051215-16788-2-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

new_cpu is reassigned below, so we do not need this here.
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1410529276.3569.24.camel@tkhaiSigned-off-by: NIngo Molnar <mingo@kernel.org>

The code in task_numa_compare() will only examine at most one idle CPU per node,
because they all have the same score. However, some idle CPUs are better
candidates than others, due to busy or idle SMT siblings, etc...

The scheduler has logic to find the best CPU within an LLC to place a
task. The NUMA code should probably use it.

This seems to reduce the standard deviation for single instance SPECjbb2005
with a low warehouse count on my 4 node test system.
Signed-off-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: mgorman@suse.de
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140904163530.189d410a@cuia.bos.redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

When running workloads on 2+ socket systems, based on perf profiles, the
update_cfs_rq_blocked_load() function often shows up as taking up a
noticeable % of run time.

Much of the contention is in __update_cfs_rq_tg_load_contrib() when we
update the tg load contribution stats.  However, it turns out that in many
cases, they don't need to be updated and "tg_contrib" is 0.

This patch adds a check in __update_cfs_rq_tg_load_contrib() to skip updating
tg load contribution stats when nothing needs to be updated. This reduces the
cacheline contention that would be unnecessary.
Reviewed-by: NBen Segall <bsegall@google.com>
Reviewed-by: NWaiman Long <Waiman.Long@hp.com>
Signed-off-by: NJason Low <jason.low2@hp.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: jason.low2@hp.com
Cc: Yuyang Du <yuyang.du@intel.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Chegu Vinod <chegu_vinod@hp.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409643684.19197.15.camel@j-VirtualBoxSigned-off-by: NIngo Molnar <mingo@kernel.org>

An overrun could happen in function start_hrtick_dl()
when a task with SCHED_DEADLINE runs in the microseconds
range.

For example, if a task with SCHED_DEADLINE has the following parameters:

  Task  runtime  deadline  period
   P1   200us     500us    500us

The deadline and period from task P1 are less than 1ms.

In order to achieve microsecond precision, we need to enable HRTICK feature
by the next command:

  PC#echo "HRTICK" > /sys/kernel/debug/sched_features
  PC#trace-cmd record -e sched_switch &
  PC#./schedtool -E -t 200000:500000:500000 -e ./test

The binary test is in an endless while(1) loop here.
Some pieces of trace.dat are as follows:

  <idle>-0   157.603157: sched_switch: :R ==> 2481:4294967295: test
  test-2481  157.603203: sched_switch:  2481:R ==> 0:120: swapper/2
  <idle>-0   157.605657: sched_switch:  :R ==> 2481:4294967295: test
  test-2481  157.608183: sched_switch:  2481:R ==> 2483:120: trace-cmd
  trace-cmd-2483 157.609656: sched_switch:2483:R==>2481:4294967295: test

We can get the runtime of P1 from the information above:

  runtime = 157.608183 - 157.605657
  runtime = 0.002526(2.526ms)

The correct runtime should be less than or equal to 200us at some point.

The problem is caused by a conditional judgment "delta > 10000"
in function start_hrtick_dl().

Because no hrtimer start up to control the rest of runtime
when the reset of runtime is less than 10us.

So the process will continue to run until tick-period is coming.

Move the code with the limit of the least time slice
from hrtick_start_fair() to hrtick_start() because the
EDF schedule class also needs this function in start_hrtick_dl().

To fix this problem, we call hrtimer_start() unconditionally in
start_hrtick_dl(), and make sure the scheduling slice won't be smaller
than 10us in hrtimer_start().
Signed-off-by: NXiaofeng Yan <xiaofeng.yan@huawei.com>
Reviewed-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NJuri Lelli <juri.lelli@arm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409022941-5880-1-git-send-email-xiaofeng.yan@huawei.com
[ Massaged the changelog and the code. ]
Signed-off-by: NIngo Molnar <mingo@kernel.org>

The use of "rcu_assign_pointer()" is NULLing out the pointer.
According to RCU_INIT_POINTER()'s block comment:

  "1.   This use of RCU_INIT_POINTER() is NULLing out the pointer"

it is better to use it instead of rcu_assign_pointer() because it has a
smaller overhead.

The following Coccinelle semantic patch was used:
 @@
 @@

 - rcu_assign_pointer
 + RCU_INIT_POINTER
   (..., NULL)
Signed-off-by: NAndreea-Cristina Bernat <bernat.ada@gmail.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: paulmck@linux.vnet.ibm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140822145043.GA580@adaSigned-off-by: NIngo Molnar <mingo@kernel.org>

__get_cpu_var can paper over differences in the definitions of
cpumask_var_t and either use the address of the cpumask variable
directly or perform a fetch of the address of the struct cpumask
allocated elsewhere. This is important particularly when using per cpu
cpumask_var_t declarations because in one case we have an offset into
a per cpu area to handle and in the other case we need to fetch a
pointer from the offset.

This patch introduces a new macro

this_cpu_cpumask_var_ptr()

that is defined where cpumask_var_t is defined and performs the proper
actions. All use cases where __get_cpu_var is used with cpumask_var_t
are converted to the use of this_cpu_cpumask_var_ptr().
Signed-off-by: NChristoph Lameter <cl@linux.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

Avoid double_rq_lock() and use TASK_ON_RQ_MIGRATING for
load_balance(). The advantage is (obviously) not holding two
rq->lock's at the same time and thereby increasing parallelism.

Further note that if there was no task to migrate we will not
have acquired the second rq->lock at all.

The important point to note is that because we acquire dst->lock
immediately after releasing src->lock the potential wait time of
task_rq_lock() callers on TASK_ON_RQ_MIGRATING is not longer
than it would have been in the double rq lock scenario.
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1408528109.23412.94.camel@tkhaiSigned-off-by: NIngo Molnar <mingo@kernel.org>

Avoid double_rq_lock() and use the TASK_ON_RQ_MIGRATING state for
active_load_balance_cpu_stop(). The advantage is (obviously) not
holding two 'rq->lock's at the same time and thereby increasing
parallelism.

Further note that if there was no task to migrate we will not
have acquired the second rq->lock at all.

The important point to note is that because we acquire dst->lock
immediately after releasing src->lock the potential wait time of
task_rq_lock() callers on TASK_ON_RQ_MIGRATING is not longer
than it would have been in the double rq lock scenario.
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1408528081.23412.92.camel@tkhaiSigned-off-by: NIngo Molnar <mingo@kernel.org>

Implement task_on_rq_queued() and use it everywhere instead of
on_rq check. No functional changes.

The only exception is we do not use the wrapper in
check_for_tasks(), because it requires to export
task_on_rq_queued() in global header files. Next patch in series
would return it back, so we do not twist it from here to there.
Signed-off-by: NKirill Tkhai <ktkhai@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1408528052.23412.87.camel@tkhaiSigned-off-by: NIngo Molnar <mingo@kernel.org>