linux.git/kernel/sched/core.c, branch v4.7-rc2

sched/core: Fix remote wakeups

2016-05-25T06:35:18+00:00

Commit:

  b5179ac70de8 ("sched/fair: Prepare to fix fairness problems on migration")

... introduced a bug: Mike Galbraith found that it introduced a
performance regression, while Paul E. McKenney reported lost
wakeups and bisected it to this commit.

The reason is that I mis-read ttwu_queue() such that I assumed any
wakeup that got a remote queue must have had the task migrated.

Since this is not so; we need to transfer this information between
queueing the wakeup and actually doing the wakeup. Use a new
task_struct::sched_flag for this, we already write to
sched_contributes_to_load in the wakeup path so this is a hot and
modified cacheline.

Reported-by: Paul E. McKenney 
Reported-by: Mike Galbraith 
Tested-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Andrew Hunter 
Cc: Andy Lutomirski 
Cc: Ben Segall 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Dave Hansen 
Cc: Denys Vlasenko 
Cc: Fenghua Yu 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Matt Fleming 
Cc: Morten Rasmussen 
Cc: Oleg Nesterov 
Cc: Paul Turner 
Cc: Pavan Kondeti 
Cc: Peter Zijlstra 
Cc: Quentin Casasnovas 
Cc: Thomas Gleixner 
Cc: byungchul.park@lge.com
Fixes: b5179ac70de8 ("sched/fair: Prepare to fix fairness problems on migration")
Link: http://lkml.kernel.org/r/20160523091907.GD15728@worktop.ger.corp.intel.com
Signed-off-by: Ingo Molnar

sched/core: Provide a tsk_nr_cpus_allowed() helper

2016-05-12T07:55:36+00:00

tsk_nr_cpus_allowed() is an accessor for task->nr_cpus_allowed which allows
us to change the representation of ->nr_cpus_allowed if required.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1462969411-17735-2-git-send-email-bigeasy@linutronix.de
Signed-off-by: Ingo Molnar

sched/nohz: Fix affine unpinned timers mess

2016-05-12T07:55:32+00:00

The following commit:

  9642d18eee2c ("nohz: Affine unpinned timers to housekeepers")'

intended to affine unpinned timers to housekeepers:

  unpinned timers(full dynaticks, idle)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(full dynaticks, busy)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(houserkeepers, idle)    =>   nearest busy housekeepers(otherwise, fallback to itself)

However, the !idle_cpu(i) && is_housekeeping_cpu(cpu) check modified the
intention to:

  unpinned timers(full dynaticks, idle)   =>   any housekeepers(no mattter cpu topology)
  unpinned timers(full dynaticks, busy)   =>   any housekeepers(no mattter cpu topology)
  unpinned timers(housekeepers, idle)     =>   any busy cpus(otherwise, fallback to any housekeepers)

This patch fixes it by checking if there are busy housekeepers nearby,
otherwise falls to any housekeepers/itself. After the patch:

  unpinned timers(full dynaticks, idle)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(full dynaticks, busy)   =>   nearest busy housekeepers(otherwise, fallback to any housekeepers)
  unpinned timers(housekeepers, idle)     =>   nearest busy housekeepers(otherwise, fallback to itself)

Signed-off-by: Wanpeng Li 
Signed-off-by: Peter Zijlstra (Intel) 
[ Fixed the changelog. ]
Cc: Frederic Weisbecker 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Fixes: 'commit 9642d18eee2c ("nohz: Affine unpinned timers to housekeepers")'
Link: http://lkml.kernel.org/r/1462344334-8303-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Ingo Molnar

sched/core: Kill sched_class::task_waking to clean up the migration logic

2016-05-12T07:55:31+00:00

With sched_class::task_waking being called only when we do
set_task_cpu(), we can make sched_class::migrate_task_rq() do the work
and eliminate sched_class::task_waking entirely.

Signed-off-by: Peter Zijlstra (Intel) 
Cc: Andrew Hunter 
Cc: Ben Segall 
Cc: Linus Torvalds 
Cc: Matt Fleming 
Cc: Mike Galbraith 
Cc: Mike Galbraith 
Cc: Morten Rasmussen 
Cc: Paul Turner 
Cc: Pavan Kondeti 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: byungchul.park@lge.com
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar

sched/fair: Prepare to fix fairness problems on migration

2016-05-12T07:55:31+00:00

Mike reported that our recent attempt to fix migration problems:

  3a47d5124a95 ("sched/fair: Fix fairness issue on migration")

broke interactivity and the signal starve test. We reverted that
commit and now let's try it again more carefully, with some other
underlying problems fixed first.

One problem is that I assumed ENQUEUE_WAKING was only set when we do a
cross-cpu wakeup (migration), which isn't true. This means we now
destroy the vruntime history of tasks and wakeup-preemption suffers.

Cure this by making my assumption true, only call
sched_class::task_waking() when we do a cross-cpu wakeup. This avoids
the indirect call in the case we do a local wakeup.

Reported-by: Mike Galbraith 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Andrew Hunter 
Cc: Ben Segall 
Cc: Linus Torvalds 
Cc: Matt Fleming 
Cc: Mike Galbraith 
Cc: Morten Rasmussen 
Cc: Paul Turner 
Cc: Pavan Kondeti 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: byungchul.park@lge.com
Cc: linux-kernel@vger.kernel.org
Fixes: 3a47d5124a95 ("sched/fair: Fix fairness issue on migration")
Signed-off-by: Ingo Molnar

Merge branch 'smp/hotplug' into sched/core, to resolve conflicts

2016-05-12T07:51:36+00:00

Conflicts:
	kernel/sched/core.c

Signed-off-by: Ingo Molnar

sched/core: Fix comment typo in wake_q_add()

2016-05-09T06:39:52+00:00

... the comment clearly refers to wake_up_q(), and not
wake_up_list().

Signed-off-by: Davidlohr Bueso 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: dave@stgolabs.net
Link: http://lkml.kernel.org/r/1462766290-28664-1-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar

sched/core: Remove unused variable

2016-05-09T06:39:52+00:00

Remove unused variable 'ret', and directly return 0.

Signed-off-by: Muhammad Falak R Wani 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1462441879-10092-1-git-send-email-falakreyaz@gmail.com
Signed-off-by: Ingo Molnar

sched: Make hrtick_notifier an explicit call

2016-05-06T12:58:26+00:00

No need for an extra notifier. We don't need to handle all these states. It's
sufficient to kill the timer when the cpu dies.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra 
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160310120025.770528462@linutronix.de
Signed-off-by: Thomas Gleixner

sched/fair: Make ilb_notifier an explicit call

2016-05-06T12:58:26+00:00

No need for an extra notifier.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra 
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160310120025.693720241@linutronix.de
Signed-off-by: Thomas Gleixner