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Microoptimize sched_pickcpu() CPU affinity on SMT.

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Use of CPU_FFS() to implement CPUSET_FOREACH() allows to save up to ~0.5%
of CPU time on 72-thread SMT system doing 80K IOPS to NVMe from one thread.

MFC after:	1 month
Sponsored by:	iXsystems, Inc.
This commit is contained in:
Alexander Motin 2019-09-26 00:35:06 +00:00
parent a631497fca
commit 176dd236dc
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=352728
1 changed files with 9 additions and 9 deletions
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18
sys/kern/sched_ule.c
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@ -643,10 +643,6 @@ struct cpu_search {
#define CPU_SEARCH_HIGHEST 0x2
#define CPU_SEARCH_BOTH (CPU_SEARCH_LOWEST|CPU_SEARCH_HIGHEST)
#define CPUSET_FOREACH(cpu, mask) \
for ((cpu) = 0; (cpu) <= mp_maxid; (cpu)++) \
if (CPU_ISSET(cpu, &mask))
static __always_inline int cpu_search(const struct cpu_group *cg,
struct cpu_search *low, struct cpu_search *high, const int match);
int __noinline cpu_search_lowest(const struct cpu_group *cg,
@ -1292,13 +1288,17 @@ sched_pickcpu(struct thread *td, int flags)
tdq->tdq_lowpri >= PRI_MIN_IDLE &&
SCHED_AFFINITY(ts, CG_SHARE_L2)) {
if (cg->cg_flags & CG_FLAG_THREAD) {
CPUSET_FOREACH(cpu, cg->cg_mask) {
if (TDQ_CPU(cpu)->tdq_lowpri < PRI_MIN_IDLE)
/* Check all SMT threads for being idle. */
for (cpu = CPU_FFS(&cg->cg_mask) - 1; ; cpu++) {
if (CPU_ISSET(cpu, &cg->cg_mask) &&
TDQ_CPU(cpu)->tdq_lowpri < PRI_MIN_IDLE)
break;
if (cpu >= mp_maxid) {
SCHED_STAT_INC(pickcpu_idle_affinity);
return (ts->ts_cpu);
}
}
} else
cpu = INT_MAX;
if (cpu > mp_maxid) {
} else {
SCHED_STAT_INC(pickcpu_idle_affinity);
return (ts->ts_cpu);
}