This simply tracks the efficiency of the recent_used_cpu. The hit rate of this matters as it can avoid a domain search. Similarly, the miss rate matters because each miss is a penalty to the fast path.
It is not required that this patch be merged with the series but if we are looking at the usefulness of p->recent_used_cpu, the stats generate hard data on what the hit rate is. MMTests uses this to generate additional metrics. SIS Recent Used Hit: A recent CPU was eligible and used. Each hit is a domain search avoided. SIS Recent Used Miss: A recent CPU was eligible but unavailable. Each time this is miss, there was a small penalty to the fast path before a domain search happened. SIS Recent Success Rate: A percentage of the number of hits versus the total attempts to use the recent CPU. SIS Recent Attempts: The total number of times the recent CPU was examined. A high number of Recent Attempts with a low Success Rate implies the fast path is being punished severely. This could have been presented as a weighting of hits and misses but calculating an appropriate weight for misses is problematic. Signed-off-by: Mel Gorman <mgor...@techsingularity.net> --- kernel/sched/debug.c | 2 ++ kernel/sched/fair.c | 23 +++++++++++++---------- kernel/sched/sched.h | 2 ++ kernel/sched/stats.c | 7 ++++--- 4 files changed, 21 insertions(+), 13 deletions(-) diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c index 2386cc5e79e5..8f933a9e8c25 100644 --- a/kernel/sched/debug.c +++ b/kernel/sched/debug.c @@ -718,6 +718,8 @@ do { \ P(sis_domain_search); P(sis_scanned); P(sis_failed); + P(sis_recent_hit); + P(sis_recent_miss); } #undef P diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 494ba01f3414..d9acd55d309b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6291,16 +6291,19 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) recent_used_cpu = p->recent_used_cpu; if (recent_used_cpu != prev && recent_used_cpu != target && - cpus_share_cache(recent_used_cpu, target) && - (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) && - cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) && - asym_fits_capacity(task_util, recent_used_cpu)) { - /* - * Replace recent_used_cpu with prev as it is a potential - * candidate for the next wake: - */ - p->recent_used_cpu = prev; - return recent_used_cpu; + cpus_share_cache(recent_used_cpu, target)) { + if ((available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) && + cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) && + asym_fits_capacity(task_util, recent_used_cpu)) { + /* + * Replace recent_used_cpu with prev as it is a potential + * candidate for the next wake: + */ + p->recent_used_cpu = prev; + schedstat_inc(this_rq()->sis_recent_hit); + return recent_used_cpu; + } + schedstat_inc(this_rq()->sis_recent_miss); } /* diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 90a62dd9293d..6a6578c4c24b 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1055,6 +1055,8 @@ struct rq { unsigned int sis_domain_search; unsigned int sis_scanned; unsigned int sis_failed; + unsigned int sis_recent_hit; + unsigned int sis_recent_miss; #endif #ifdef CONFIG_CPU_IDLE diff --git a/kernel/sched/stats.c b/kernel/sched/stats.c index 390bfcc3842c..402fab75aa14 100644 --- a/kernel/sched/stats.c +++ b/kernel/sched/stats.c @@ -10,7 +10,7 @@ * Bump this up when changing the output format or the meaning of an existing * format, so that tools can adapt (or abort) */ -#define SCHEDSTAT_VERSION 16 +#define SCHEDSTAT_VERSION 17 static int show_schedstat(struct seq_file *seq, void *v) { @@ -30,14 +30,15 @@ static int show_schedstat(struct seq_file *seq, void *v) /* runqueue-specific stats */ seq_printf(seq, - "cpu%d %u 0 %u %u %u %u %llu %llu %lu %u %u %u %u", + "cpu%d %u 0 %u %u %u %u %llu %llu %lu %u %u %u %u %u %u", cpu, rq->yld_count, rq->sched_count, rq->sched_goidle, rq->ttwu_count, rq->ttwu_local, rq->rq_cpu_time, rq->rq_sched_info.run_delay, rq->rq_sched_info.pcount, rq->sis_search, rq->sis_domain_search, - rq->sis_scanned, rq->sis_failed); + rq->sis_scanned, rq->sis_failed, + rq->sis_recent_hit, rq->sis_recent_miss); seq_printf(seq, "\n"); -- 2.26.2