path: root/kernel
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authorSteve Muckle <smuckle@google.com>2018-08-31 15:42:17 -0700
committerIngo Molnar <mingo@kernel.org>2018-09-10 10:13:47 +0200
commitd0cdb3ce8834332d918fc9c8ff74f8a169ec9abe (patch)
treec27b8f02c8c9d801f8a5123832f7637fe57dbe92 /kernel
parent12b04875d666e83d27511df25580de84505bc758 (diff)
sched/fair: Fix vruntime_normalized() for remote non-migration wakeup
When a task which previously ran on a given CPU is remotely queued to wake up on that same CPU, there is a period where the task's state is TASK_WAKING and its vruntime is not normalized. This is not accounted for in vruntime_normalized() which will cause an error in the task's vruntime if it is switched from the fair class during this time. For example if it is boosted to RT priority via rt_mutex_setprio(), rq->min_vruntime will not be subtracted from the task's vruntime but it will be added again when the task returns to the fair class. The task's vruntime will have been erroneously doubled and the effective priority of the task will be reduced. Note this will also lead to inflation of all vruntimes since the doubled vruntime value will become the rq's min_vruntime when other tasks leave the rq. This leads to repeated doubling of the vruntime and priority penalty. Fix this by recognizing a WAKING task's vruntime as normalized only if sched_remote_wakeup is true. This indicates a migration, in which case the vruntime would have been normalized in migrate_task_rq_fair(). Based on a similar patch from John Dias <joaodias@google.com>. Suggested-by: Peter Zijlstra <peterz@infradead.org> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Signed-off-by: Steve Muckle <smuckle@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Chris Redpath <Chris.Redpath@arm.com> Cc: John Dias <joaodias@google.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Miguel de Dios <migueldedios@google.com> Cc: Morten Rasmussen <Morten.Rasmussen@arm.com> Cc: Patrick Bellasi <Patrick.Bellasi@arm.com> Cc: Paul Turner <pjt@google.com> Cc: Quentin Perret <quentin.perret@arm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Todd Kjos <tkjos@google.com> Cc: kernel-team@android.com Fixes: b5179ac70de8 ("sched/fair: Prepare to fix fairness problems on migration") Link: http://lkml.kernel.org/r/20180831224217.169476-1-smuckle@google.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8cff8d55ee95..c6b7d6daab20 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9644,7 +9644,8 @@ static inline bool vruntime_normalized(struct task_struct *p)
* - A task which has been woken up by try_to_wake_up() and
* waiting for actually being woken up by sched_ttwu_pending().
- if (!se->sum_exec_runtime || p->state == TASK_WAKING)
+ if (!se->sum_exec_runtime ||
+ (p->state == TASK_WAKING && p->sched_remote_wakeup))
return true;
return false;