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
