yield_to() is supposed to return -ESRCH if there is no task to
yield to, but because the type is bool that is the same as returning
true.

The only place I see which cares is kvm_vcpu_on_spin().
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NRaghavendra <raghavendra.kt@linux.vnet.ibm.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org
Link: http://lkml.kernel.org/r/20140523102042.GA7267@mwandaSigned-off-by: NIngo Molnar <mingo@kernel.org>

To be future-proof and for better readability the time comparisons are modified
to use time_after() instead of plain, error-prone math.
Signed-off-by: NManuel Schölling <manuel.schoelling@gmx.de>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1400780723-24626-1-git-send-email-manuel.schoelling@gmx.deSigned-off-by: NIngo Molnar <mingo@kernel.org>

The current no_hz idle load balancer do load balancing for *all* idle cpus,
even though the time due to load balance for a particular
idle cpu could be still a while in the future.  This introduces a much
higher load balancing rate than what is necessary.  The patch
changes the behavior by only doing idle load balancing on
behalf of an idle cpu only when it is due for load balancing.

On SGI's systems with over 3000 cores, the cpu responsible for idle balancing
got overwhelmed with idle balancing, and introduces a lot of OS noise
to workloads.  This patch fixes the issue.
Signed-off-by: NTim Chen <tim.c.chen@linux.intel.com>
Acked-by: NRuss Anderson <rja@sgi.com>
Reviewed-by: NRik van Riel <riel@redhat.com>
Reviewed-by: NJason Low <jason.low2@hp.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Len Brown <len.brown@intel.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Cc: Hedi Berriche <hedi@sgi.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: MichelLespinasse <walken@google.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1400621967.2970.280.camel@schen9-DESKSigned-off-by: NIngo Molnar <mingo@kernel.org>

sched_cfs_period_timer() reads cfs_b->period without locks before calling
do_sched_cfs_period_timer(), and similarly unthrottle_offline_cfs_rqs()
would read cfs_b->period without the right lock. Thus a simultaneous
change of bandwidth could cause corruption on any platform where ktime_t
or u64 writes/reads are not atomic.

Extend cfs_b->lock from do_sched_cfs_period_timer() to include the read of
cfs_b->period to solve that issue; unthrottle_offline_cfs_rqs() can just
use 1 rather than the exact quota, much like distribute_cfs_runtime()
does.

There is also an unlocked read of cfs_b->runtime_expires, but a race
there would only delay runtime expiry by a tick. Still, the comparison
should just be != anyway, which clarifies even that problem.
Signed-off-by: NBen Segall <bsegall@google.com>
Tested-by: NRoman Gushchin <klamm@yandex-team.ru>
[peterz: Fix compile warn]
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140519224945.20303.93530.stgit@sword-of-the-dawn.mtv.corp.google.com
Cc: pjt@google.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Affine wakeups have the potential to interfere with NUMA placement.
If a task wakes up too many other tasks, affine wakeups will get
disabled.

However, regardless of how many other tasks it wakes up, it gets
re-enabled once a second, potentially interfering with NUMA
placement of other tasks.

By decaying wakee_wakes in half instead of zeroing it, we can avoid
that problem for some workloads.
Signed-off-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: chegu_vinod@hp.com
Cc: umgwanakikbuti@gmail.com
Link: http://lkml.kernel.org/r/20140516001332.67f91af2@annuminas.surriel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Update the migrate_improves/degrades_locality() functions with
knowledge of pseudo-interleaving.

Do not consider moving tasks around within the set of group's active
nodes as improving or degrading locality. Instead, leave the load
balancer free to balance the load between a numa_group's active nodes.

Also, switch from the group/task_weight functions to the group/task_fault
functions. The "weight" functions involve a division, but both calls use
the same divisor, so there's no point in doing that from these functions.

On a 4 node (x10 core) system, performance of SPECjbb2005 seems
unaffected, though the number of migrations with 2 8-warehouse wide
instances seems to have almost halved, due to the scheduler running
each instance on a single node.
Signed-off-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: mgorman@suse.de
Cc: chegu_vinod@hp.com
Link: http://lkml.kernel.org/r/20140515130306.61aae7db@cuia.bos.redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Currently the NUMA balancing code only allows moving tasks between NUMA
nodes when the load on both nodes is in balance. This breaks down when
the load was imbalanced to begin with.

Allow tasks to be moved between NUMA nodes if the imbalance is small,
or if the new imbalance is be smaller than the original one.
Suggested-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: mgorman@suse.de
Cc: chegu_vinod@hp.com
Signed-off-by: NIngo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/20140514132221.274b3463@annuminas.surriel.com

sched/rt: Fix 'struct sched_dl_entity' and dl_task_time() comments, to match the current upstream code
Signed-off-by: Nxiaofeng.yan <xiaofeng.yan@huawei.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1399605687-18094-1-git-send-email-xiaofeng.yan@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

sched: Consolidate open coded implementations of nice level frobbing into nice_to_rlimit() and rlimit_to_nice()
Signed-off-by: NDongsheng Yang <yangds.fnst@cn.fujitsu.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/a568a1e3cc8e78648f41b5035fa5e381d36274da.1399532322.git.yangds.fnst@cn.fujitsu.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

If the sched_clock time starts at a large value, the kernel will spin
in sched_avg_update for a long time while rq->age_stamp catches up
with rq->clock.

The comment in kernel/sched/clock.c says that there is no strict promise
that it starts at zero.  So initialize rq->age_stamp when a cpu starts up
to avoid this.

I was seeing long delays on a simulator that didn't start the clock at
zero.  This might also be an issue on reboots on processors that don't
re-initialize the timer to zero on reset, and when using kexec.
Signed-off-by: NCorey Minyard <cminyard@mvista.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1399574859-11714-1-git-send-email-minyard@acm.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Sometimes ->nr_running may cross 2 but interrupt is not being
sent to rq's cpu. In this case we don't reenable the timer.
Looks like this may be the reason for rare unexpected effects,
if nohz is enabled.

Patch replaces all places of direct changing of nr_running
and makes add_nr_running() caring about crossing border.
Signed-off-by: NKirill Tkhai <tkhai@yandex.ru>
Acked-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140508225830.2469.97461.stgit@localhostSigned-off-by: NIngo Molnar <mingo@kernel.org>

Currently, in idle_balance(), we update rq->next_balance when we pull_tasks.
However, it is also important to update this in the !pulled_tasks case too.

When the CPU is "busy" (the CPU isn't idle), rq->next_balance gets computed
using sd->busy_factor (so we increase the balance interval when the CPU is
busy). However, when the CPU goes idle, rq->next_balance could still be set
to a large value that was computed with the sd->busy_factor.

Thus, we need to also update rq->next_balance in idle_balance() in the cases
where !pulled_tasks too, so that rq->next_balance gets updated without taking
the busy_factor into account when the CPU is about to go idle.

This patch makes rq->next_balance get updated independently of whether or
not we pulled_task. Also, we add logic to ensure that we always traverse
at least 1 of the sched domains to get a proper next_balance value for
updating rq->next_balance.

Additionally, since load_balance() modifies the sd->balance_interval, we
need to re-obtain the sched domain's interval after the call to
load_balance() in rebalance_domains() before we update rq->next_balance.

This patch adds and uses 2 new helper functions, update_next_balance() and
get_sd_balance_interval() to update next_balance and obtain the sched
domain's balance_interval.
Signed-off-by: NJason Low <jason.low2@hp.com>
Reviewed-by: NPreeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: daniel.lezcano@linaro.org
Cc: alex.shi@linaro.org
Cc: efault@gmx.de
Cc: vincent.guittot@linaro.org
Cc: morten.rasmussen@arm.com
Cc: aswin@hp.com
Link: http://lkml.kernel.org/r/1399596562.2200.7.camel@j-VirtualBoxSigned-off-by: NIngo Molnar <mingo@kernel.org>

Suggested-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NDongsheng Yang <yangds.fnst@cn.fujitsu.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1399541715-19568-1-git-send-email-yangds.fnst@cn.fujitsu.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

There is no need to zero struct sched_group member cpumask and struct
sched_group_power member power since both structures are already allocated
as zeroed memory in __sdt_alloc().

This patch has been tested with
BUG_ON(!cpumask_empty(sched_group_cpus(sg))); and BUG_ON(sg->sgp->power);
in build_sched_groups() on ARM TC2 and INTEL i5 M520 platform including
CPU hotplug scenarios.
Signed-off-by: NDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1398865178-12577-1-git-send-email-dietmar.eggemann@arm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Jet Chen has reported a kernel panics when booting qemu-system-x86_64 with
kvm64 cpu. A panic occured while building the sched_domain.

In sched_init_numa, we create a new topology table in which both default
levels and numa levels are copied. The last row of the table must have a null
pointer in the mask field.

The current implementation doesn't add this last row in the computation of the
table size. So we add 1 row in the allocation size that will be used as the
last row of the table. The kzalloc will ensure that the mask field is NULL.
Reported-by: NJet Chen <jet.chen@intel.com>
Tested-by: NJet Chen <jet.chen@intel.com>
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: fengguang.wu@intel.com
Link: http://lkml.kernel.org/r/1399972261-25693-1-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

On smaller systems, the top level sched domain will be an affine
domain, and select_idle_sibling is invoked for every SD_WAKE_AFFINE
wakeup. This seems to be working well.

On larger systems, with the node distance between far away NUMA nodes
being > RECLAIM_DISTANCE, select_idle_sibling is only called if the
waker and the wakee are on nodes less than RECLAIM_DISTANCE apart.

This patch leaves in place the policy of not pulling the task across
nodes on such systems, while fixing the issue that select_idle_sibling
is not called at all in certain circumstances.

The code will look for an idle CPU in the same CPU package as the
CPU where the task ran previously.
Signed-off-by: NRik van Riel <riel@redhat.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: morten.rasmussen@arm.com
Cc: george.mccollister@gmail.com
Cc: ktkhai@parallels.com
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Link: http://lkml.kernel.org/r/20140514114037.2d93266f@annuminas.surriel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Gotos are chained pointlessly here, and the 'out' label
can be dispensed with.
Signed-off-by: NMichael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/536CEC29.9090503@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

The logic in this function is a little contorted, clean it up:

  * Rather than having chained gotos for the -EFBIG case, just
    return -EFBIG directly.

  * Now, the label 'out' is no longer needed, and 'ret' must be zero
    zero by the time we fall through to this point, so just return 0.
Signed-off-by: NMichael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/536CEC24.9080201@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

task_hot checks exec_start on any runnable task, but if it has been
migrated since the it last ran, then exec_start is a clock_task from
another cpu. If the old cpu's clock_task was sufficiently far ahead of
this cpu's then the task will not be considered for another migration
until it has run. Instead reset exec_start whenever a task is migrated,
since it is presumably no longer hot anyway.
Signed-off-by: NBen Segall <bsegall@google.com>
[ Made it compile. ]
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140515225920.7179.13924.stgit@sword-of-the-dawn.mtv.corp.google.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Lai found that:

  WARNING: CPU: 1 PID: 13 at arch/x86/kernel/smp.c:124 native_smp_send_reschedule+0x2d/0x4b()
  ...
  migration_cpu_stop+0x1d/0x22

was caused by set_cpus_allowed_ptr() assuming that cpu_active_mask is
always a sub-set of cpu_online_mask.

This isn't true since 5fbd036b ("sched: Cleanup cpu_active madness").

So set active and online at the same time to avoid this particular
problem.

Fixes: 5fbd036b ("sched: Cleanup cpu_active madness")
Signed-off-by: NLai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael wang <wangyun@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Toshi Kani <toshi.kani@hp.com>
Link: http://lkml.kernel.org/r/53758B12.8060609@cn.fujitsu.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Tejun reported that his resume was failing due to order-3 allocations
from sched_domain building.

Replace the NR_CPUS arrays in there with a dynamically allocated
array.
Reported-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-7cysnkw1gik45r864t1nkudh@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Tejun reported that his resume was failing due to order-3 allocations
from sched_domain building.

Replace the NR_CPUS arrays in there with a dynamically allocated
array.
Reported-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NJuri Lelli <juri.lelli@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-kat4gl1m5a6dwy6nzuqox45e@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Michael Kerrisk noticed that creating SCHED_DEADLINE reservations
with certain parameters (e.g, a runtime of something near 2^64 ns)
can cause a system freeze for some amount of time.

The problem is that in the interface we have

 u64 sched_runtime;

while internally we need to have a signed runtime (to cope with
budget overruns)

 s64 runtime;

At the time we setup a new dl_entity we copy the first value in
the second. The cast turns out with negative values when
sched_runtime is too big, and this causes the scheduler to go crazy
right from the start.

Moreover, considering how we deal with deadlines wraparound

 (s64)(a - b) < 0

we also have to restrict acceptable values for sched_{deadline,period}.

This patch fixes the thing checking that user parameters are always
below 2^63 ns (still large enough for everyone).

It also rewrites other conditions that we check, since in
__checkparam_dl we don't have to deal with deadline wraparounds
and what we have now erroneously fails when the difference between
values is too big.
Reported-by: NMichael Kerrisk <mtk.manpages@gmail.com>
Suggested-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Cc: Dario Faggioli<raistlin@linux.it>
Cc: Dave Jones <davej@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140513141131.20d944f81633ee937f256385@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

The way we read POSIX one should only call sched_getparam() when
sched_getscheduler() returns either SCHED_FIFO or SCHED_RR.

Given that we currently return sched_param::sched_priority=0 for all
others, extend the same behaviour to SCHED_DEADLINE.
Requested-by: NMichael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NMichael Kerrisk <mtk.manpages@gmail.com>
Cc: Dario Faggioli <raistlin@linux.it>
Cc: linux-man <linux-man@vger.kernel.org>
Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20140512205034.GH13467@laptop.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

The scheduler uses policy=-1 to preserve the current policy state to
implement sys_sched_setparam(), this got exposed to userspace by
accident through sys_sched_setattr(), cure this.
Reported-by: NMichael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NMichael Kerrisk <mtk.manpages@gmail.com>
Cc: <stable@vger.kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140509085311.GJ30445@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

The documented[1] behavior of sched_attr() in the proposed man page text is:

    sched_attr::size must be set to the size of the structure, as in
    sizeof(struct sched_attr), if the provided structure is smaller
    than the kernel structure, any additional fields are assumed
    '0'. If the provided structure is larger than the kernel structure,
    the kernel verifies all additional fields are '0' if not the
    syscall will fail with -E2BIG.

As currently implemented, sched_copy_attr() returns -EFBIG for
for this case, but the logic in sys_sched_setattr() converts that
error to -EFAULT. This patch fixes the behavior.

[1] http://thread.gmane.org/gmane.linux.kernel/1615615/focus=1697760Signed-off-by: NMichael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/536CEC17.9070903@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

The only value ever returned by cpuidle_idle_call() is 0 and its
only caller ignores that value anyway, so make it void.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/4717784.WmVEpDoliM@vostro.rjw.lanSigned-off-by: NIngo Molnar <mingo@kernel.org>

Apply goto to reduce lines and nesting levels.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NNicolas Pitre <nicolas.pitre@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-cc6vb0snt3sr7op6rlbfeqfh@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

With the generic idle functions assuming !polling we should only clear
the polling bit at the very last opportunity in order to avoid
spurious IPIs.

Ideally we'd flip the default to polling, but that means auditing all
arch idle functions.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NNicolas Pitre <nicolas.pitre@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-vq7719foqzf6z5h4j7eh7f9e@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Because mwait_idle_with_hints() gets called from !idle context it must
call current_clr_polling(). This however means that resched_task() is
very likely to send an IPI even when we were polling:

  CPU0					CPU1

  if (current_set_polling_and_test())
    goto out;

  __monitor(&ti->flags);
  if (!need_resched())
    __mwait(eax, ecx);
					set_tsk_need_resched(p);
					smp_mb();
out:
  current_clr_polling();
					if (!tsk_is_polling(p))
					  smp_send_reschedule(cpu);

So while it is correct (extra IPIs aren't a problem, whereas a missed
IPI would be) it is a performance problem (for some).

Avoid this issue by using fetch_or() to atomically set NEED_RESCHED
and test if POLLING_NRFLAG is set.

Since a CPU stuck in mwait is unlikely to modify the flags word,
contention on the cmpxchg is unlikely and thus we should mostly
succeed in a single go.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Acked-by: NNicolas Pitre <nico@linaro.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-kf5suce6njh5xf5d3od13rr0@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

It was found that when running some workloads (such as AIM7) on large
systems with many cores, CPUs do not remain idle for long. Thus, tasks
can wake/get enqueued while doing idle balancing.

In this patch, while traversing the domains in idle balance, in
addition to checking for pulled_task, we add an extra check for
this_rq->nr_running for determining if we should stop searching for
tasks to pull. If there are runnable tasks on this rq, then we will
stop traversing the domains. This reduces the chance that idle balance
delays a task from running.

This patch resulted in approximately a 6% performance improvement when
running a Java Server workload on an 8 socket machine.
Signed-off-by: NJason Low <jason.low2@hp.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: daniel.lezcano@linaro.org
Cc: alex.shi@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: efault@gmx.de
Cc: vincent.guittot@linaro.org
Cc: morten.rasmussen@arm.com
Cc: aswin@hp.com
Cc: chegu_vinod@hp.com
Link: http://lkml.kernel.org/r/1398303035-18255-4-git-send-email-jason.low2@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

A new flag SD_SHARE_POWERDOMAIN is created to reflect whether groups of CPUs
in a sched_domain level can or not reach different power state. As an example,
the flag should be cleared at CPU level if groups of cores can be power gated
independently. This information can be used in the load balance decision or to
add load balancing level between group of CPUs that can power gate
independantly.
This flag is part of the topology flags that can be set by arch.
Reviewed-by: NDietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: NDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: tony.luck@intel.com
Cc: fenghua.yu@intel.com
Cc: schwidefsky@de.ibm.com
Cc: cmetcalf@tilera.com
Cc: benh@kernel.crashing.org
Cc: preeti@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1397209481-28542-5-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Create a dedicated topology table for handling asymetric feature of powerpc.
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: NPreeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Andy Fleming <afleming@freescale.com>
Cc: Anton Blanchard <anton@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Preeti U. Murthy <preeti@linux.vnet.ibm.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: Vasant Hegde <hegdevasant@linux.vnet.ibm.com>
Cc: tony.luck@intel.com
Cc: fenghua.yu@intel.com
Cc: schwidefsky@de.ibm.com
Cc: cmetcalf@tilera.com
Cc: dietmar.eggemann@arm.com
Cc: devicetree@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1397209481-28542-4-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

BOOK level is only relevant for s390 so we create a dedicated topology table
with BOOK level and remove it from default table.
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Philipp Hachtmann <phacht@linux.vnet.ibm.com>
Cc: cmetcalf@tilera.com
Cc: benh@kernel.crashing.org
Cc: dietmar.eggemann@arm.com
Cc: preeti@linux.vnet.ibm.com
Cc: tony.luck@intel.com
Cc: fenghua.yu@intel.com
Cc: linux390@de.ibm.com
Cc: linux-s390@vger.kernel.org
Link: http://lkml.kernel.org/r/1397209481-28542-3-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

We replace the old way to configure the scheduler topology with a new method
which enables a platform to declare additionnal level (if needed).

We still have a default topology table definition that can be used by platform
that don't want more level than the SMT, MC, CPU and NUMA ones. This table can
be overwritten by an arch which either wants to add new level where a load
balance make sense like BOOK or powergating level or wants to change the flags
configuration of some levels.

For each level, we need a function pointer that returns cpumask for each cpu,
a function pointer that returns the flags for the level and a name. Only flags
that describe topology, can be set by an architecture. The current topology
flags are:

 SD_SHARE_CPUPOWER
 SD_SHARE_PKG_RESOURCES
 SD_NUMA
 SD_ASYM_PACKING

Then, each level must be a subset on the next one. The build sequence of the
sched_domain will take care of removing useless levels like those with 1 CPU
and those with the same CPU span and no more relevant information for
load balancing than its children.
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Tested-by: NDietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: NPreeti U Murthy <preeti@linux.vnet.ibm.com>
Reviewed-by: NDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux390@de.ibm.com
Cc: linux-ia64@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Link: http://lkml.kernel.org/r/1397209481-28542-2-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Setting the numa_preferred_node for a task in task_numa_migrate
does nothing on a 2-node system. Either we migrate to the node
that already was our preferred node, or we stay where we were.

On a 4-node system, it can slightly decrease overhead, by not
calling the NUMA code as much. Since every node tends to be
directly connected to every other node, running on the wrong
node for a while does not do much damage.

However, on an 8 node system, there are far more bad nodes
than there are good ones, and pretending that a second choice
is actually the preferred node can greatly delay, or even
prevent, a workload from converging.

The only time we can safely pretend that a second choice
node is the preferred node is when the task is part of a
workload that spans multiple NUMA nodes.
Signed-off-by: NRik van Riel <riel@redhat.com>
Tested-by: NVinod Chegu <chegu_vinod@hp.com>
Acked-by: NMel Gorman <mgorman@suse.de>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1397235629-16328-4-git-send-email-riel@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

When tasks have not converged on their preferred nodes yet, we want
to retry fairly often, to make sure we do not migrate a task's memory
to an undesirable location, only to have to move it again later.

This patch reduces the interval at which migration is retried,
when the task's numa_scan_period is small.
Signed-off-by: NRik van Riel <riel@redhat.com>
Tested-by: NVinod Chegu <chegu_vinod@hp.com>
Acked-by: NMel Gorman <mgorman@suse.de>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1397235629-16328-3-git-send-email-riel@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

The NUMA code is smart enough to distribute the memory of workloads
that span multiple NUMA nodes across those NUMA nodes.

However, it still has a pretty high scan rate for such workloads,
because any memory that is left on a node other than the node of
the CPU that faulted on the memory is counted as non-local, which
causes the scan rate to go up.

Counting the memory on any node where the task's numa group is
actively running as local, allows the scan rate to slow down
once the application is settled in.

This should reduce the overhead of the automatic NUMA placement
code, when a workload spans multiple NUMA nodes.
Signed-off-by: NRik van Riel <riel@redhat.com>
Tested-by: NVinod Chegu <chegu_vinod@hp.com>
Acked-by: NMel Gorman <mgorman@suse.de>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1397235629-16328-2-git-send-email-riel@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Also initialize the per-sd variables for newidle load balancing
in sd_numa_init().
Signed-off-by: NJason Low <jason.low2@hp.com>
Acked-by: morten.rasmussen@arm.com
Cc: daniel.lezcano@linaro.org
Cc: alex.shi@linaro.org
Cc: preeti@linux.vnet.ibm.com
Cc: efault@gmx.de
Cc: vincent.guittot@linaro.org
Cc: aswin@hp.com
Cc: chegu_vinod@hp.com
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1398303035-18255-3-git-send-email-jason.low2@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

The following commit:

  e5fc6611 ("sched: Fix race in idle_balance()")

can potentially cause rq->max_idle_balance_cost to not be updated,
even when load_balance(NEWLY_IDLE) is attempted and the per-sd
max cost value is updated.

Preeti noticed a similar issue with updating rq->next_balance.

In this patch, we fix this by making sure we still check/update those values
even if a task gets enqueued while browsing the domains.
Signed-off-by: NJason Low <jason.low2@hp.com>
Reviewed-by: NPreeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: morten.rasmussen@arm.com
Cc: aswin@hp.com
Cc: daniel.lezcano@linaro.org
Cc: alex.shi@linaro.org
Cc: efault@gmx.de
Cc: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/1398725155-7591-2-git-send-email-jason.low2@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>