Commit-ID: b7e7ade34e6188bee2e3b0d42b51d25137d9e2a5 Gitweb: http://git.kernel.org/tip/b7e7ade34e6188bee2e3b0d42b51d25137d9e2a5 Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Mon, 23 May 2016 11:19:07 +0200 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Wed, 25 May 2016 08:35:18 +0200
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 <paul...@linux.vnet.ibm.com> Reported-by: Mike Galbraith <umgwanakikb...@gmail.com> Tested-by: Mike Galbraith <umgwanakikb...@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Andrew Hunter <a...@google.com> Cc: Andy Lutomirski <l...@amacapital.net> Cc: Ben Segall <bseg...@google.com> Cc: Borislav Petkov <b...@alien8.de> Cc: Brian Gerst <brge...@gmail.com> Cc: Dave Hansen <dave.han...@linux.intel.com> Cc: Denys Vlasenko <dvlas...@redhat.com> Cc: Fenghua Yu <fenghua...@intel.com> Cc: H. Peter Anvin <h...@zytor.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Matt Fleming <m...@codeblueprint.co.uk> Cc: Morten Rasmussen <morten.rasmus...@arm.com> Cc: Oleg Nesterov <o...@redhat.com> Cc: Paul Turner <p...@google.com> Cc: Pavan Kondeti <pkond...@codeaurora.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Quentin Casasnovas <quentin.casasno...@oracle.com> Cc: Thomas Gleixner <t...@linutronix.de> Cc: byungchul.p...@lge.com Fixes: b5179ac70de8 ("sched/fair: Prepare to fix fairness problems on migration") Link: http://lkml.kernel.org/r/20160523091907.gd15...@worktop.ger.corp.intel.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- include/linux/sched.h | 1 + kernel/sched/core.c | 18 +++++++++++------- 2 files changed, 12 insertions(+), 7 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 6cc0df9..e053517 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1533,6 +1533,7 @@ struct task_struct { unsigned sched_reset_on_fork:1; unsigned sched_contributes_to_load:1; unsigned sched_migrated:1; + unsigned sched_remote_wakeup:1; unsigned :0; /* force alignment to the next boundary */ /* unserialized, strictly 'current' */ diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 404c078..7f2cae4 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