With the introduction of sched_attr::sched_nice we need to check
if we've got permission to actually change the nice value.

Daniel found that can_nice() would always fail; and upon
inspection it turns out that can_nice() only tests to see if we
can lower the nice value, but it doesn't validate if we're
lowering or not.

Therefore amend the test to only call can_nice() when we lower
the nice value.
Reported-and-Tested-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: raistlin@linux.it
Cc: juri.lelli@gmail.com
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Fixes: d50dde5a ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Link: http://lkml.kernel.org/r/20140116165425.GA9481@laptop.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

"futexes: Increase hash table size for better performance"
introduces a new alloc_large_system_hash() call.

alloc_large_system_hash() however may allocate less memory than
requested, e.g. limited by MAX_ORDER.

Hence pass a pointer to alloc_large_system_hash() which will
contain the hash shift when the function returns. Afterwards
correctly set futex_hashsize.

Fixes a crash on s390 where the requested allocation size was
4MB but only 1MB was allocated.
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Waiman Long <Waiman.Long@hp.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Davidlohr Bueso <davidlohr@hp.com>
Link: http://lkml.kernel.org/r/20140116135450.GA4345@osirisSigned-off-by: NIngo Molnar <mingo@kernel.org>

I noticed the new sched_{set,get}attr() calls didn't properly deal
with the SCHED_RESET_ON_FORK hack.

Instead of propagating the flags in high bits nonsense use the brand
spanking new attr::sched_flags field.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Dario Faggioli <raistlin@linux.it>
Link: http://lkml.kernel.org/r/20140115162242.GJ31570@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

Fengguang Wu reported the following build warning:

  > kernel/sched/core.c:3067 __sched_setscheduler() warn: unsigned 'attr->sched_priority' is never less than zero.

Since it doesn't make sense for attr::sched_priority to be negative,
remove the check, since we already test for an upper limit any actual
negative values passed in through the old param::sched_priority field
will still be detected.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Dario Faggioli <raistlin@linux.it>
Fixes: d50dde5a ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Link: http://lkml.kernel.org/n/tip-fid9nalzii2r5voxtf4eh5kz@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Wu reported LTP failures:

  > ltp.sched_setparam02.1.TFAIL
  > ltp.sched_setparam02.2.TFAIL
  > ltp.sched_setparam02.3.TFAIL
  > ltp.sched_setparam03.1.TFAIL

There were 2 things wrong; firstly __setscheduler() failed on
sched_setparam()'s policy = -1, fix that by reading from p->policy in
that case.

Secondly, getparam() (and getattr()) would still report !0
sched_priority for !FIFO/RR tasks after having been such. So
unconditionally set p->rt_priority.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Dario Faggioli <raistlin@linux.it>
Fixes: d50dde5a ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Link: http://lkml.kernel.org/r/20140115153320.GH31570@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

Previously sched_setscheduler() and sched_setparam() would not affect
the nice value of a task, restore this behaviour.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: raistlin@linux.it
Cc: juri.lelli@gmail.com
Cc: Michael wang <wangyun@linux.vnet.ibm.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Fixes: d50dde5a ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Link: http://lkml.kernel.org/r/20140115113015.GB31570@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

Fengguang Wu's kbuild test robot reported the following new htmldocs warnings:

  >>> Warning(kernel/sched/core.c:3380): No description found for parameter 'uattr'
  >>> Warning(kernel/sched/core.c:3380): Excess function parameter 'attr' description in 'sys_sched_setattr'
  >>> Warning(kernel/sched/core.c:3520): No description found for parameter 'uattr'
  >>> Warning(kernel/sched/core.c:3520): Excess function parameter 'attr' description in 'sys_sched_getattr'

The second argument to sys_sched_{setattr,getattr}() is named uattr (not attr).
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Dario Faggioli <raistlin@linux.it>
Fixes: d50dde5a ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Link: http://lkml.kernel.org/r/52D5552D.5000102@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Dan Carpenter reported new 'Smatch' warnings:

  > tree:   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/core
  > head:   130816ce
  > commit: 1baca4ce [17/50] sched/deadline: Add SCHED_DEADLINE SMP-related data structures & logic
  >
  > kernel/sched/deadline.c:937 pick_next_task_dl() warn: variable dereferenced before check 'p' (see line 934)

BUG_ON() already fires if pick_next_dl_entity() doesn't return a valid
dl_se. No need to check if p is valid afterward.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Fixes: 1baca4ce ("sched/deadline: Add SCHED_DEADLINE SMP-related data structures & logic")
Link: http://lkml.kernel.org/r/52D54E25.6060100@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

fix these new sparse warnings:

  >> kernel/sched/core.c:305:14: sparse: symbol 'sysctl_sched_dl_period' was not declared. Should it be static?
  >> kernel/sched/core.c:306:5: sparse: symbol 'sysctl_sched_dl_runtime' was not declared. Should it be static?

Better still, they're completely unused so remove them.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Link: http://lkml.kernel.org/n/tip-ke0shkG7vMnzmcdqhhiymyem@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

new sparse warnings:

  >> kernel/sched/cpudeadline.c:38:6: sparse: symbol 'cpudl_exchange' was not declared. Should it be static?
  >> kernel/sched/cpudeadline.c:46:6: sparse: symbol 'cpudl_heapify' was not declared. Should it be static?
  >> kernel/sched/cpudeadline.c:71:6: sparse: symbol 'cpudl_change_key' was not declared. Should it be static?
  >> kernel/sched/cpudeadline.c:195:15: sparse: memset with byte count of 163928
Signed-off-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Fixes: 6bfd6d72 ("sched/deadline: speed up SCHED_DEADLINE pushes with a push-heap")
Link: http://lkml.kernel.org/r/52d47f8c.EYJsA5+mELPBk4t6\%fengguang.wu@intel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

With various drivers wanting to inject idle time; we get people
calling idle routines outside of the idle loop proper.

Therefore we need to be extra careful about not missing
TIF_NEED_RESCHED -> PREEMPT_NEED_RESCHED propagations.

While looking at this, I also realized there's a small window in the
existing idle loop where we can miss TIF_NEED_RESCHED; when it hits
right after the tif_need_resched() test at the end of the loop but
right before the need_resched() test at the start of the loop.

So move preempt_fold_need_resched() out of the loop where we're
guaranteed to have TIF_NEED_RESCHED set.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-x9jgh45oeayzajz2mjt0y7d6@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Currently local_bh_disable() is out-of-line for no apparent reason.
So inline it to save a few cycles on call/return nonsense, the
function body is a single add on x86 (a few loads and store extra on
load/store archs).

Also expose two new local_bh functions:

  __local_bh_{dis,en}able_ip(unsigned long ip, unsigned int cnt);

Which implement the actual local_bh_{dis,en}able() behaviour.

The next patch uses the exposed @cnt argument to optimize bh lock
functions.

With build fixes from Jacob Pan.

Cc: rjw@rjwysocki.net
Cc: rui.zhang@intel.com
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: hpa@zytor.com
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: lenb@kernel.org
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20131119151338.GF3694@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

The below tells us the static_key conversion has a problem; since the
exact point of clearing that flag isn't too important, delay the flip
and use a workqueue to process it.

[ ] TSC synchronization [CPU#0 -> CPU#22]:
[ ] Measured 8 cycles TSC warp between CPUs, turning off TSC clock.
[ ]
[ ] ======================================================
[ ] [ INFO: possible circular locking dependency detected ]
[ ] 3.13.0-rc3-01745-g848b0d0322cb-dirty #637 Not tainted
[ ] -------------------------------------------------------
[ ] swapper/0/1 is trying to acquire lock:
[ ]  (jump_label_mutex){+.+...}, at: [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ]
[ ] but task is already holding lock:
[ ]  (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8109408b>] cpu_hotplug_begin+0x2b/0x60
[ ]
[ ] which lock already depends on the new lock.
[ ]
[ ]
[ ] the existing dependency chain (in reverse order) is:
[ ]
[ ] -> #1 (cpu_hotplug.lock){+.+.+.}:
[ ]        [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ]        [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ]        [<ffffffff81093fdc>] get_online_cpus+0x3c/0x60
[ ]        [<ffffffff8104cc67>] arch_jump_label_transform+0x37/0x130
[ ]        [<ffffffff8115a3cf>] __jump_label_update+0x5f/0x80
[ ]        [<ffffffff8115a48d>] jump_label_update+0x9d/0xb0
[ ]        [<ffffffff8115aa6d>] static_key_slow_inc+0x9d/0xb0
[ ]        [<ffffffff810c0f65>] sched_feat_set+0xf5/0x100
[ ]        [<ffffffff810c5bdc>] set_numabalancing_state+0x2c/0x30
[ ]        [<ffffffff81d12f3d>] numa_policy_init+0x1af/0x1b7
[ ]        [<ffffffff81cebdf4>] start_kernel+0x35d/0x41f
[ ]        [<ffffffff81ceb5a5>] x86_64_start_reservations+0x2a/0x2c
[ ]        [<ffffffff81ceb6a2>] x86_64_start_kernel+0xfb/0xfe
[ ]
[ ] -> #0 (jump_label_mutex){+.+...}:
[ ]        [<ffffffff810de141>] __lock_acquire+0x1701/0x1eb0
[ ]        [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ]        [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ]        [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ]        [<ffffffff8115aa3b>] static_key_slow_inc+0x6b/0xb0
[ ]        [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ]        [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ]        [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ]        [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ]        [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ]        [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ]        [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ]        [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ]        [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ]        [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ]
[ ] other info that might help us debug this:
[ ]
[ ]  Possible unsafe locking scenario:
[ ]
[ ]        CPU0                    CPU1
[ ]        ----                    ----
[ ]   lock(cpu_hotplug.lock);
[ ]                                lock(jump_label_mutex);
[ ]                                lock(cpu_hotplug.lock);
[ ]   lock(jump_label_mutex);
[ ]
[ ]  *** DEADLOCK ***
[ ]
[ ] 2 locks held by swapper/0/1:
[ ]  #0:  (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff81094037>] cpu_maps_update_begin+0x17/0x20
[ ]  #1:  (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8109408b>] cpu_hotplug_begin+0x2b/0x60
[ ]
[ ] stack backtrace:
[ ] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc3-01745-g848b0d0322cb-dirty #637
[ ] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010
[ ]  ffffffff82c9c270 ffff880236843bb8 ffffffff8165c5f5 ffffffff82c9c270
[ ]  ffff880236843bf8 ffffffff81658c02 ffff880236843c80 ffff8802368586a0
[ ]  ffff880236858678 0000000000000001 0000000000000002 ffff880236858000
[ ] Call Trace:
[ ]  [<ffffffff8165c5f5>] dump_stack+0x4e/0x7a
[ ]  [<ffffffff81658c02>] print_circular_bug+0x1f9/0x207
[ ]  [<ffffffff810de141>] __lock_acquire+0x1701/0x1eb0
[ ]  [<ffffffff816680ff>] ? __atomic_notifier_call_chain+0x8f/0xb0
[ ]  [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ]  [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ]  [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ]  [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ]  [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ]  [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ]  [<ffffffff8115aa3b>] static_key_slow_inc+0x6b/0xb0
[ ]  [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ]  [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ]  [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ]  [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ]  [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ]  [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ]  [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ]  [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ]  [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ]  [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ]  [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ]  [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] ------------[ cut here ]------------
[ ] WARNING: CPU: 0 PID: 1 at /usr/src/linux-2.6/kernel/smp.c:374 smp_call_function_many+0xad/0x300()
[ ] Modules linked in:
[ ] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc3-01745-g848b0d0322cb-dirty #637
[ ] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010
[ ]  0000000000000009 ffff880236843be0 ffffffff8165c5f5 0000000000000000
[ ]  ffff880236843c18 ffffffff81093d8c 0000000000000000 0000000000000000
[ ]  ffffffff81ccd1a0 ffffffff810ca951 0000000000000000 ffff880236843c28
[ ] Call Trace:
[ ]  [<ffffffff8165c5f5>] dump_stack+0x4e/0x7a
[ ]  [<ffffffff81093d8c>] warn_slowpath_common+0x8c/0xc0
[ ]  [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ]  [<ffffffff81093dda>] warn_slowpath_null+0x1a/0x20
[ ]  [<ffffffff8110b72d>] smp_call_function_many+0xad/0x300
[ ]  [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ]  [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ]  [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ]  [<ffffffff8110ba96>] smp_call_function+0x46/0x80
[ ]  [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ]  [<ffffffff8110bb3c>] on_each_cpu+0x3c/0xa0
[ ]  [<ffffffff810ca950>] ? sched_clock_idle_sleep_event+0x20/0x20
[ ]  [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ]  [<ffffffff8104f964>] text_poke_bp+0x64/0xd0
[ ]  [<ffffffff810ca950>] ? sched_clock_idle_sleep_event+0x20/0x20
[ ]  [<ffffffff8104ccde>] arch_jump_label_transform+0xae/0x130
[ ]  [<ffffffff8115a3cf>] __jump_label_update+0x5f/0x80
[ ]  [<ffffffff8115a48d>] jump_label_update+0x9d/0xb0
[ ]  [<ffffffff8115aa6d>] static_key_slow_inc+0x9d/0xb0
[ ]  [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ]  [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ]  [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ]  [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ]  [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ]  [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ]  [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ]  [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ]  [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ]  [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ]  [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ]  [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] ---[ end trace 6ff1df5620c49d26 ]---
[ ] tsc: Marking TSC unstable due to check_tsc_sync_source failed
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-v55fgqj3nnyqnngmvuu8ep6h@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

In order to avoid the runtime condition and variable load turn
sched_clock_stable into a static_key.

Also provide a shorter implementation of local_clock() and
cpu_clock(int) when sched_clock_stable==1.

                        MAINLINE   PRE       POST

    sched_clock_stable: 1          1         1
    (cold) sched_clock: 329841     221876    215295
    (cold) local_clock: 301773     234692    220773
    (warm) sched_clock: 38375      25602     25659
    (warm) local_clock: 100371     33265     27242
    (warm) rdtsc:       27340      24214     24208
    sched_clock_stable: 0          0         0
    (cold) sched_clock: 382634     235941    237019
    (cold) local_clock: 396890     297017    294819
    (warm) sched_clock: 38194      25233     25609
    (warm) local_clock: 143452     71234     71232
    (warm) rdtsc:       27345      24245     24243
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-eummbdechzz37mwmpags1gjr@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Now that x86 no longer requires IRQs disabled for sched_clock() and
ia64 never had this requirement (it doesn't seem to do cpufreq at
all), we can remove the requirement of disabling IRQs.

                        MAINLINE   PRE        POST

    sched_clock_stable: 1          1          1
    (cold) sched_clock: 329841     257223     221876
    (cold) local_clock: 301773     309889     234692
    (warm) sched_clock: 38375      25280      25602
    (warm) local_clock: 100371     85268      33265
    (warm) rdtsc:       27340      24247      24214
    sched_clock_stable: 0          0          0
    (cold) sched_clock: 382634     301224     235941
    (cold) local_clock: 396890     399870     297017
    (warm) sched_clock: 38194      25630      25233
    (warm) local_clock: 143452     129629     71234
    (warm) rdtsc:       27345      24307      24245
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-36e5kohiasnr106d077mgubp@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Currently all _bh_ lock functions do two preempt_count operations:

  local_bh_disable();
  preempt_disable();

and for the unlock:

  preempt_enable_no_resched();
  local_bh_enable();

Since its a waste of perfectly good cycles to modify the same variable
twice when you can do it in one go; use the new
__local_bh_{dis,en}able_ip() functions that allow us to provide a
preempt_count value to add/sub.

So define SOFTIRQ_LOCK_OFFSET as the offset a _bh_ lock needs to
add/sub to be done in one go.

As a bonus it gets rid of the preempt_enable_no_resched() usage.

This reduces a 1000 loops of:

  spin_lock_bh(&bh_lock);
  spin_unlock_bh(&bh_lock);

from 53596 cycles to 51995 cycles. I didn't do enough measurements to
say for absolute sure that the result is significant but the the few
runs I did for each suggest it is so.
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: hpa@zytor.com
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: lenb@kernel.org
Cc: rjw@rjwysocki.net
Cc: rui.zhang@intel.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20131119151338.GF3694@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

The test on_null_domain is done twice in the trigger_load_balance function.

Move the test at the begin of the function, so there is only one check.
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1389008085-9069-9-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The cpu information is stored in the struct rq. Pass the struct rq to
nohz_idle_balance, so all the functions called in run_rebalance_domains have
the same parameters and the 'this_cpu' variable becomes pointless.
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
[ Added !SMP build fix. ]
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1389008085-9069-8-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The cpu information is stored in the struct rq and the caller of the
rebalance_domains function pass the cpu to retrieve the struct rq but
it already has the struct rq info. Replace the cpu parameter with the
struct rq.
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1389008085-9069-7-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The cpu parameter is no longer needed in nohz_balancer_kick, let's remove
the parameter.
Reviewed-by: NPreeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1389008085-9069-6-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The 'call_cpu' is never used in the function. Remove it.
Reviewed-by: NPreeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1389008085-9069-5-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The on_null_domain() function is getting the cpu to retrieve the struct rq
associated with it.

Pass 'struct rq' directly to the function as the caller already has the info.
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1389008085-9069-4-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The cpu information is already stored in the struct rq, so no need to pass it
as parameter to the nohz_kick_needed function.

The caller of this function just called idle_cpu() before to fill the
rq->idle_balance field.

Use rq->cpu and rq->idle_balance.
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1389008085-9069-3-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The cpu information is already stored in the struct rq, so no need to pass it
as parameter to the trigger_load_balance function.

Cc: linaro-kernel@lists.linaro.org
Cc: preeti.lkml@gmail.com
Cc: mingo@redhat.com
Cc: peterz@infradead.org
Signed-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1389008085-9069-2-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

The current hotplug admission control is broken because:

  CPU_DYING -> migration_call() -> migrate_tasks() -> __migrate_task()

cannot fail and hard assumes it _will_ move all tasks off of the dying
cpu, failing this will break hotplug.

The much simpler solution is a DOWN_PREPARE handler that fails when
removing one CPU gets us below the total allocated bandwidth.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20131220171343.GL2480@laptop.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>

Remove the deadline specific sysctls for now. The problem with them is
that the interaction with the exisiting rt knobs is nearly impossible
to get right.

The current (as per before this patch) situation is that the rt and dl
bandwidth is completely separate and we enforce rt+dl < 100%. This is
undesirable because this means that the rt default of 95% leaves us
hardly any room, even though dl tasks are saver than rt tasks.

Another proposed solution was (a discarted patch) to have the dl
bandwidth be a fraction of the rt bandwidth. This is highly
confusing imo.

Furthermore neither proposal is consistent with the situation we
actually want; which is rt tasks ran from a dl server. In which case
the rt bandwidth is a direct subset of dl.

So whichever way we go, the introduction of dl controls at this point
is painful. Therefore remove them and instead share the rt budget.

This means that for now the rt knobs are used for dl admission control
and the dl runtime is accounted against the rt runtime. I realise that
this isn't entirely desirable either; but whatever we do we appear to
need to change the interface later, so better have a small interface
for now.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-zpyqbqds1r0vyxtxza1e7rdc@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

For now deadline tasks are not allowed to set smp affinity; however
the current tests are wrong, cure this.

The test in __sched_setscheduler() also uses an on-stack cpumask_t
which is a no-no.

Change both tests to use cpumask_subset() such that we test the root
domain span to be a subset of the cpus_allowed mask. This way we're
sure the tasks can always run on all CPUs they can be balanced over,
and have no effective affinity constraints.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-fyqtb1lapxca3lhsxv9cumdc@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Data from tests confirmed that the original active load balancing
logic didn't scale neither in the number of CPU nor in the number of
tasks (as sched_rt does).

Here we provide a global data structure to keep track of deadlines
of the running tasks in the system. The structure is composed by
a bitmask showing the free CPUs and a max-heap, needed when the system
is heavily loaded.

The implementation and concurrent access scheme are kept simple by
design. However, our measurements show that we can compete with sched_rt
on large multi-CPUs machines [1].

Only the push path is addressed, the extension to use this structure
also for pull decisions is straightforward. However, we are currently
evaluating different (in order to decrease/avoid contention) data
structures to solve possibly both problems. We are also going to re-run
tests considering recent changes inside cpupri [2].

 [1] http://retis.sssup.it/~jlelli/papers/Ospert11Lelli.pdf
 [2] http://www.spinics.net/lists/linux-rt-users/msg06778.htmlSigned-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-14-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

In order of deadline scheduling to be effective and useful, it is
important that some method of having the allocation of the available
CPU bandwidth to tasks and task groups under control.
This is usually called "admission control" and if it is not performed
at all, no guarantee can be given on the actual scheduling of the
-deadline tasks.

Since when RT-throttling has been introduced each task group have a
bandwidth associated to itself, calculated as a certain amount of
runtime over a period. Moreover, to make it possible to manipulate
such bandwidth, readable/writable controls have been added to both
procfs (for system wide settings) and cgroupfs (for per-group
settings).

Therefore, the same interface is being used for controlling the
bandwidth distrubution to -deadline tasks and task groups, i.e.,
new controls but with similar names, equivalent meaning and with
the same usage paradigm are added.

However, more discussion is needed in order to figure out how
we want to manage SCHED_DEADLINE bandwidth at the task group level.
Therefore, this patch adds a less sophisticated, but actually
very sensible, mechanism to ensure that a certain utilization
cap is not overcome per each root_domain (the single rq for !SMP
configurations).

Another main difference between deadline bandwidth management and
RT-throttling is that -deadline tasks have bandwidth on their own
(while -rt ones doesn't!), and thus we don't need an higher level
throttling mechanism to enforce the desired bandwidth.

This patch, therefore:

 - adds system wide deadline bandwidth management by means of:
    * /proc/sys/kernel/sched_dl_runtime_us,
    * /proc/sys/kernel/sched_dl_period_us,
   that determine (i.e., runtime / period) the total bandwidth
   available on each CPU of each root_domain for -deadline tasks;

 - couples the RT and deadline bandwidth management, i.e., enforces
   that the sum of how much bandwidth is being devoted to -rt
   -deadline tasks to stay below 100%.

This means that, for a root_domain comprising M CPUs, -deadline tasks
can be created until the sum of their bandwidths stay below:

    M * (sched_dl_runtime_us / sched_dl_period_us)

It is also possible to disable this bandwidth management logic, and
be thus free of oversubscribing the system up to any arbitrary level.
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-12-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Some method to deal with rt-mutexes and make sched_dl interact with
the current PI-coded is needed, raising all but trivial issues, that
needs (according to us) to be solved with some restructuring of
the pi-code (i.e., going toward a proxy execution-ish implementation).

This is under development, in the meanwhile, as a temporary solution,
what this commits does is:

 - ensure a pi-lock owner with waiters is never throttled down. Instead,
   when it runs out of runtime, it immediately gets replenished and it's
   deadline is postponed;

 - the scheduling parameters (relative deadline and default runtime)
   used for that replenishments --during the whole period it holds the
   pi-lock-- are the ones of the waiting task with earliest deadline.

Acting this way, we provide some kind of boosting to the lock-owner,
still by using the existing (actually, slightly modified by the previous
commit) pi-architecture.

We would stress the fact that this is only a surely needed, all but
clean solution to the problem. In the end it's only a way to re-start
discussion within the community. So, as always, comments, ideas, rants,
etc.. are welcome! :-)
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
[ Added !RT_MUTEXES build fix. ]
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-11-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Turn the pi-chains from plist to rb-tree, in the rt_mutex code,
and provide a proper comparison function for -deadline and
-priority tasks.

This is done mainly because:
 - classical prio field of the plist is just an int, which might
   not be enough for representing a deadline;
 - manipulating such a list would become O(nr_deadline_tasks),
   which might be to much, as the number of -deadline task increases.

Therefore, an rb-tree is used, and tasks are queued in it according
to the following logic:
 - among two -priority (i.e., SCHED_BATCH/OTHER/RR/FIFO) tasks, the
   one with the higher (lower, actually!) prio wins;
 - among a -priority and a -deadline task, the latter always wins;
 - among two -deadline tasks, the one with the earliest deadline
   wins.

Queueing and dequeueing functions are changed accordingly, for both
the list of a task's pi-waiters and the list of tasks blocked on
a pi-lock.
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-again-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-10-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

It is very likely that systems that wants/needs to use the new
SCHED_DEADLINE policy also want to have the scheduling latency of
the -deadline tasks under control.

For this reason a new version of the scheduling wakeup latency,
called "wakeup_dl", is introduced.

As a consequence of applying this patch there will be three wakeup
latency tracer:

 * "wakeup", that deals with all tasks in the system;
 * "wakeup_rt", that deals with -rt and -deadline tasks only;
 * "wakeup_dl", that deals with -deadline tasks only.
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-9-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Make it possible to specify a period (different or equal than
deadline) for -deadline tasks. Relative deadlines (D_i) are used on
task arrivals to generate new scheduling (absolute) deadlines as "d =
t + D_i", and periods (P_i) to postpone the scheduling deadlines as "d
= d + P_i" when the budget is zero.

This is in general useful to model (and schedule) tasks that have slow
activation rates (long periods), but have to be scheduled soon once
activated (short deadlines).
Signed-off-by: NHarald Gustafsson <harald.gustafsson@ericsson.com>
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-7-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Make the core scheduler and load balancer aware of the load
produced by -deadline tasks, by updating the moving average
like for sched_rt.
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-6-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Introduces data structures relevant for implementing dynamic
migration of -deadline tasks and the logic for checking if
runqueues are overloaded with -deadline tasks and for choosing
where a task should migrate, when it is the case.

Adds also dynamic migrations to SCHED_DEADLINE, so that tasks can
be moved among CPUs when necessary. It is also possible to bind a
task to a (set of) CPU(s), thus restricting its capability of
migrating, or forbidding migrations at all.

The very same approach used in sched_rt is utilised:
 - -deadline tasks are kept into CPU-specific runqueues,
 - -deadline tasks are migrated among runqueues to achieve the
   following:
    * on an M-CPU system the M earliest deadline ready tasks
      are always running;
    * affinity/cpusets settings of all the -deadline tasks is
      always respected.

Therefore, this very special form of "load balancing" is done with
an active method, i.e., the scheduler pushes or pulls tasks between
runqueues when they are woken up and/or (de)scheduled.
IOW, every time a preemption occurs, the descheduled task might be sent
to some other CPU (depending on its deadline) to continue executing
(push). On the other hand, every time a CPU becomes idle, it might pull
the second earliest deadline ready task from some other CPU.

To enforce this, a pull operation is always attempted before taking any
scheduling decision (pre_schedule()), as well as a push one after each
scheduling decision (post_schedule()). In addition, when a task arrives
or wakes up, the best CPU where to resume it is selected taking into
account its affinity mask, the system topology, but also its deadline.
E.g., from the scheduling point of view, the best CPU where to wake
up (and also where to push) a task is the one which is running the task
with the latest deadline among the M executing ones.

In order to facilitate these decisions, per-runqueue "caching" of the
deadlines of the currently running and of the first ready task is used.
Queued but not running tasks are also parked in another rb-tree to
speed-up pushes.
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-5-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Introduces the data structures, constants and symbols needed for
SCHED_DEADLINE implementation.

Core data structure of SCHED_DEADLINE are defined, along with their
initializers. Hooks for checking if a task belong to the new policy
are also added where they are needed.

Adds a scheduling class, in sched/dl.c and a new policy called
SCHED_DEADLINE. It is an implementation of the Earliest Deadline
First (EDF) scheduling algorithm, augmented with a mechanism (called
Constant Bandwidth Server, CBS) that makes it possible to isolate
the behaviour of tasks between each other.

The typical -deadline task will be made up of a computation phase
(instance) which is activated on a periodic or sporadic fashion. The
expected (maximum) duration of such computation is called the task's
runtime; the time interval by which each instance need to be completed
is called the task's relative deadline. The task's absolute deadline
is dynamically calculated as the time instant a task (better, an
instance) activates plus the relative deadline.

The EDF algorithms selects the task with the smallest absolute
deadline as the one to be executed first, while the CBS ensures each
task to run for at most its runtime every (relative) deadline
length time interval, avoiding any interference between different
tasks (bandwidth isolation).
Thanks to this feature, also tasks that do not strictly comply with
the computational model sketched above can effectively use the new
policy.

To summarize, this patch:
 - introduces the data structures, constants and symbols needed;
 - implements the core logic of the scheduling algorithm in the new
   scheduling class file;
 - provides all the glue code between the new scheduling class and
   the core scheduler and refines the interactions between sched/dl
   and the other existing scheduling classes.
Signed-off-by: NDario Faggioli <raistlin@linux.it>
Signed-off-by: NMichael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: NFabio Checconi <fchecconi@gmail.com>
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-4-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Add the syscalls needed for supporting scheduling algorithms
with extended scheduling parameters (e.g., SCHED_DEADLINE).

In general, it makes possible to specify a periodic/sporadic task,
that executes for a given amount of runtime at each instance, and is
scheduled according to the urgency of their own timing constraints,
i.e.:

 - a (maximum/typical) instance execution time,
 - a minimum interval between consecutive instances,
 - a time constraint by which each instance must be completed.

Thus, both the data structure that holds the scheduling parameters of
the tasks and the system calls dealing with it must be extended.
Unfortunately, modifying the existing struct sched_param would break
the ABI and result in potentially serious compatibility issues with
legacy binaries.

For these reasons, this patch:

 - defines the new struct sched_attr, containing all the fields
   that are necessary for specifying a task in the computational
   model described above;

 - defines and implements the new scheduling related syscalls that
   manipulate it, i.e., sched_setattr() and sched_getattr().

Syscalls are introduced for x86 (32 and 64 bits) and ARM only, as a
proof of concept and for developing and testing purposes. Making them
available on other architectures is straightforward.

Since no "user" for these new parameters is introduced in this patch,
the implementation of the new system calls is just identical to their
already existing counterpart. Future patches that implement scheduling
policies able to exploit the new data structure must also take care of
modifying the sched_*attr() calls accordingly with their own purposes.
Signed-off-by: NDario Faggioli <raistlin@linux.it>
[ Rewrote to use sched_attr. ]
Signed-off-by: NJuri Lelli <juri.lelli@gmail.com>
[ Removed sched_setscheduler2() for now. ]
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-3-git-send-email-juri.lelli@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

In futex_wake() there is clearly no point in taking the hb->lock
if we know beforehand that there are no tasks to be woken. While
the hash bucket's plist head is a cheap way of knowing this, we
cannot rely 100% on it as there is a racy window between the
futex_wait call and when the task is actually added to the
plist. To this end, we couple it with the spinlock check as
tasks trying to enter the critical region are most likely
potential waiters that will be added to the plist, thus
preventing tasks sleeping forever if wakers don't acknowledge
all possible waiters.

Furthermore, the futex ordering guarantees are preserved,
ensuring that waiters either observe the changed user space
value before blocking or is woken by a concurrent waker. For
wakers, this is done by relying on the barriers in
get_futex_key_refs() -- for archs that do not have implicit mb
in atomic_inc(), we explicitly add them through a new
futex_get_mm function. For waiters we rely on the fact that
spin_lock calls already update the head counter, so spinners
are visible even if the lock hasn't been acquired yet.

For more details please refer to the updated comments in the
code and related discussion:

  https://lkml.org/lkml/2013/11/26/556

Special thanks to tglx for careful review and feedback.
Suggested-by: NLinus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: NDarren Hart <dvhart@linux.intel.com>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NDavidlohr Bueso <davidlohr@hp.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Scott Norton <scott.norton@hp.com>
Cc: Tom Vaden <tom.vaden@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Waiman Long <Waiman.Long@hp.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1389569486-25487-5-git-send-email-davidlohr@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

That's essential, if you want to hack on futexes.
Reviewed-by: NDarren Hart <dvhart@linux.intel.com>
Reviewed-by: NPeter Zijlstra <peterz@infradead.org>
Reviewed-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NDavidlohr Bueso <davidlohr@hp.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Scott Norton <scott.norton@hp.com>
Cc: Tom Vaden <tom.vaden@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Waiman Long <Waiman.Long@hp.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1389569486-25487-4-git-send-email-davidlohr@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Currently, the futex global hash table suffers from its fixed,
smallish (for today's standards) size of 256 entries, as well as
its lack of NUMA awareness. Large systems, using many futexes,
can be prone to high amounts of collisions; where these futexes
hash to the same bucket and lead to extra contention on the same
hb->lock. Furthermore, cacheline bouncing is a reality when we
have multiple hb->locks residing on the same cacheline and
different futexes hash to adjacent buckets.

This patch keeps the current static size of 16 entries for small
systems, or otherwise, 256 * ncpus (or larger as we need to
round the number to a power of 2). Note that this number of CPUs
accounts for all CPUs that can ever be available in the system,
taking into consideration things like hotpluging. While we do
impose extra overhead at bootup by making the hash table larger,
this is a one time thing, and does not shadow the benefits of
this patch.

Furthermore, as suggested by tglx, by cache aligning the hash
buckets we can avoid access across cacheline boundaries and also
avoid massive cache line bouncing if multiple cpus are hammering
away at different hash buckets which happen to reside in the
same cache line.

Also, similar to other core kernel components (pid, dcache,
tcp), by using alloc_large_system_hash() we benefit from its
NUMA awareness and thus the table is distributed among the nodes
instead of in a single one.

For a custom microbenchmark that pounds on the uaddr hashing --
making the wait path fail at futex_wait_setup() returning
-EWOULDBLOCK for large amounts of futexes, we can see the
following benefits on a 80-core, 8-socket 1Tb server:

 +---------+--------------------+------------------------+-----------------------+-------------------------------+
 | threads | baseline (ops/sec) | aligned-only (ops/sec) | large table (ops/sec) | large table+aligned (ops/sec) |
 +---------+--------------------+------------------------+-----------------------+-------------------------------+
 |     512 |              32426 | 50531  (+55.8%)        | 255274  (+687.2%)     | 292553  (+802.2%)             |
 |     256 |              65360 | 99588  (+52.3%)        | 443563  (+578.6%)     | 508088  (+677.3%)             |
 |     128 |             125635 | 200075 (+59.2%)        | 742613  (+491.1%)     | 835452  (+564.9%)             |
 |      80 |             193559 | 323425 (+67.1%)        | 1028147 (+431.1%)     | 1130304 (+483.9%)             |
 |      64 |             247667 | 443740 (+79.1%)        | 997300  (+302.6%)     | 1145494 (+362.5%)             |
 |      32 |             628412 | 721401 (+14.7%)        | 965996  (+53.7%)      | 1122115 (+78.5%)              |
 +---------+--------------------+------------------------+-----------------------+-------------------------------+
Reviewed-by: NDarren Hart <dvhart@linux.intel.com>
Reviewed-by: NPeter Zijlstra <peterz@infradead.org>
Reviewed-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NWaiman Long <Waiman.Long@hp.com>
Reviewed-and-tested-by: NJason Low <jason.low2@hp.com>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NDavidlohr Bueso <davidlohr@hp.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Scott Norton <scott.norton@hp.com>
Cc: Tom Vaden <tom.vaden@hp.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Link: http://lkml.kernel.org/r/1389569486-25487-3-git-send-email-davidlohr@hp.comSigned-off-by: NIngo Molnar <mingo@kernel.org>