Author: mav
Date: Sun Sep 14 22:13:19 2014
New Revision: 271604
URL: http://svnweb.freebsd.org/changeset/base/271604
Log:
Add couple memory barries to serialize tdq_cpu_idle and tdq_load accesses.
This change fixes transient performance drops in some of my benchmarks,
vanishing as soon as I am trying to collect any stats from the scheduler.
It looks like reordered access to those variables sometimes caused loss of
IPI_PREEMPT, that delayed thread execution until some later interrupt.
MFC after: 3 days
Modified:
head/sys/kern/sched_ule.c
Modified: head/sys/kern/sched_ule.c
==============================================================================
--- head/sys/kern/sched_ule.c Sun Sep 14 22:10:35 2014 (r271603)
+++ head/sys/kern/sched_ule.c Sun Sep 14 22:13:19 2014 (r271604)
@@ -1037,6 +1037,7 @@ tdq_notify(struct tdq *tdq, struct threa
ctd = pcpu_find(cpu)->pc_curthread;
if (!sched_shouldpreempt(pri, ctd->td_priority, 1))
return;
+ mb();
if (TD_IS_IDLETHREAD(ctd)) {
/*
* If the MD code has an idle wakeup routine try that before
@@ -2640,6 +2641,7 @@ sched_idletd(void *dummy)
/* Run main MD idle handler. */
tdq->tdq_cpu_idle = 1;
+ mb();
cpu_idle(switchcnt * 4 > sched_idlespinthresh);
tdq->tdq_cpu_idle = 0;
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