From: Mel Gorman <mgorman@techsingularity.net>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Aubrey Li <aubrey.li@linux.intel.com>,
Barry Song <song.bao.hua@hisilicon.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Ziljstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Linux-ARM <linux-arm-kernel@lists.infradead.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 02/10] sched/fair: Track efficiency of task recent_used_cpu
Date: Thu, 3 Dec 2020 14:11:16 +0000 [thread overview]
Message-ID: <20201203141124.7391-3-mgorman@techsingularity.net> (raw)
In-Reply-To: <20201203141124.7391-1-mgorman@techsingularity.net>
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 <mgorman@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
next prev parent reply other threads:[~2020-12-03 14:12 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-03 14:11 [RFC PATCH 00/10] Reduce time complexity of select_idle_sibling Mel Gorman
2020-12-03 14:11 ` [PATCH 01/10] sched/fair: Track efficiency " Mel Gorman
2020-12-03 14:11 ` Mel Gorman [this message]
2020-12-03 14:11 ` [PATCH 03/10] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2020-12-03 14:11 ` [PATCH 04/10] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Mel Gorman
2020-12-03 16:35 ` Vincent Guittot
2020-12-03 17:50 ` Mel Gorman
2020-12-03 14:11 ` [PATCH 05/10] sched/fair: Do not replace recent_used_cpu with the new target Mel Gorman
2020-12-03 14:11 ` [PATCH 06/10] sched/fair: Clear the target CPU from the cpumask of CPUs searched Mel Gorman
2020-12-03 16:38 ` Vincent Guittot
2020-12-03 17:52 ` Mel Gorman
2020-12-04 10:56 ` Vincent Guittot
2020-12-04 11:30 ` Mel Gorman
2020-12-04 13:13 ` Vincent Guittot
2020-12-04 13:17 ` Vincent Guittot
2020-12-04 13:40 ` Li, Aubrey
2020-12-04 13:47 ` Li, Aubrey
2020-12-04 13:47 ` Vincent Guittot
2020-12-04 14:07 ` Li, Aubrey
2020-12-04 14:31 ` Mel Gorman
2020-12-04 15:23 ` Vincent Guittot
2020-12-04 15:40 ` Mel Gorman
2020-12-04 15:43 ` Vincent Guittot
2020-12-04 18:41 ` Mel Gorman
2020-12-04 14:27 ` Mel Gorman
2020-12-03 14:11 ` [PATCH 07/10] sched/fair: Account for the idle cpu/smt search cost Mel Gorman
2020-12-03 14:11 ` [PATCH 08/10] sched/fair: Reintroduce SIS_AVG_CPU but in the context of SIS_PROP to reduce search depth Mel Gorman
2020-12-03 14:11 ` [PATCH 09/10] sched/fair: Limit the search for an idle core Mel Gorman
2020-12-03 14:19 ` Mel Gorman
2020-12-03 14:20 ` [PATCH 10/10] sched/fair: Avoid revisiting CPUs multiple times during select_idle_sibling Mel Gorman
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