Date: Wed, 24 Oct 2012 18:36:41 +0000 (UTC) From: Jim Harris <jimharris@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r242014 - head/sys/kern Message-ID: <201210241836.q9OIafqo073002@svn.freebsd.org>
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Author: jimharris Date: Wed Oct 24 18:36:41 2012 New Revision: 242014 URL: http://svn.freebsd.org/changeset/base/242014 Log: Pad tdq_lock to avoid false sharing with tdq_load and tdq_cpu_idle. This enables CPU searches (which read tdq_load) to operate independently of any contention on the spinlock. Some scheduler-intensive workloads running on an 8C single-socket SNB Xeon show considerable improvement with this change (2-3% perf improvement, 5-6% decrease in CPU util). Sponsored by: Intel Reviewed by: jeff Modified: head/sys/kern/sched_ule.c Modified: head/sys/kern/sched_ule.c ============================================================================== --- head/sys/kern/sched_ule.c Wed Oct 24 18:33:44 2012 (r242013) +++ head/sys/kern/sched_ule.c Wed Oct 24 18:36:41 2012 (r242014) @@ -223,8 +223,13 @@ static int sched_idlespinthresh = -1; * locking in sched_pickcpu(); */ struct tdq { - /* Ordered to improve efficiency of cpu_search() and switch(). */ + /* + * Ordered to improve efficiency of cpu_search() and switch(). + * tdq_lock is padded to avoid false sharing with tdq_load and + * tdq_cpu_idle. + */ struct mtx tdq_lock; /* run queue lock. */ + char pad[64 - sizeof(struct mtx)]; struct cpu_group *tdq_cg; /* Pointer to cpu topology. */ volatile int tdq_load; /* Aggregate load. */ volatile int tdq_cpu_idle; /* cpu_idle() is active. */
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