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Pad tdq_lock to avoid false sharing with tdq_load and tdq_cpu_idle.

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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
This commit is contained in:
Jim Harris 2012-10-24 18:36:41 +00:00
parent da1fc67f8a
commit 39f819e2fc
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=242014
1 changed files with 6 additions and 1 deletions
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7
sys/kern/sched_ule.c
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@ -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. */