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authorPeter Zijlstra <peterz@infradead.org>2016-05-23 11:19:07 +0200
committerIngo Molnar <mingo@kernel.org>2016-05-25 08:35:18 +0200
commitb7e7ade34e6188bee2e3b0d42b51d25137d9e2a5 (patch)
tree7cb4526b1902a93c7197a3c11150e616d565f0d5 /kernel
parent2e636d5e66c35dfcbaf617aa8fa963f6847478fe (diff)
downloadlinux-sh-b7e7ade34e6188bee2e3b0d42b51d25137d9e2a5.tar.gz
sched/core: Fix remote wakeups
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 <paulmck@linux.vnet.ibm.com> Reported-by: Mike Galbraith <umgwanakikbuti@gmail.com> Tested-by: Mike Galbraith <umgwanakikbuti@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Hunter <ahh@google.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Ben Segall <bsegall@google.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Matt Fleming <matt@codeblueprint.co.uk> Cc: Morten Rasmussen <morten.rasmussen@arm.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paul Turner <pjt@google.com> Cc: Pavan Kondeti <pkondeti@codeaurora.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com> Cc: Thomas Gleixner <tglx@linutronix.de> 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 <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/core.c18
1 files changed, 11 insertions, 7 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 404c0784b1fc..7f2cae4620c7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1768,13 +1768,15 @@ void sched_ttwu_pending(void)
cookie = lockdep_pin_lock(&rq->lock);
while (llist) {
+ int wake_flags = 0;
+
p = llist_entry(llist, struct task_struct, wake_entry);
llist = llist_next(llist);
- /*
- * See ttwu_queue(); we only call ttwu_queue_remote() when
- * its a x-cpu wakeup.
- */
- ttwu_do_activate(rq, p, WF_MIGRATED, cookie);
+
+ if (p->sched_remote_wakeup)
+ wake_flags = WF_MIGRATED;
+
+ ttwu_do_activate(rq, p, wake_flags, cookie);
}
lockdep_unpin_lock(&rq->lock, cookie);
@@ -1819,10 +1821,12 @@ void scheduler_ipi(void)
irq_exit();
}
-static void ttwu_queue_remote(struct task_struct *p, int cpu)
+static void ttwu_queue_remote(struct task_struct *p, int cpu, int wake_flags)
{
struct rq *rq = cpu_rq(cpu);
+ p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);
+
if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list)) {
if (!set_nr_if_polling(rq->idle))
smp_send_reschedule(cpu);
@@ -1869,7 +1873,7 @@ static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
#if defined(CONFIG_SMP)
if (sched_feat(TTWU_QUEUE) && !cpus_share_cache(smp_processor_id(), cpu)) {
sched_clock_cpu(cpu); /* sync clocks x-cpu */
- ttwu_queue_remote(p, cpu);
+ ttwu_queue_remote(p, cpu, wake_flags);
return;
}
#endif