From: Mel Gorman <mgorman@techsingularity.net>
To: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Phil Auld <pauld@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 2/4] sched/fair: Track efficiency of task recent_used_cpu
Date: Fri, 20 Mar 2020 15:12:43 +0000 [thread overview]
Message-ID: <20200320151245.21152-3-mgorman@techsingularity.net> (raw)
In-Reply-To: <20200320151245.21152-1-mgorman@techsingularity.net>
This simply tracks the efficiency of p->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. 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 hit, there was a 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 | 21 ++++++++++++---------
kernel/sched/sched.h | 2 ++
kernel/sched/stats.c | 7 ++++---
4 files changed, 20 insertions(+), 12 deletions(-)
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 7af6e8a12f40..d58f333bb739 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -665,6 +665,8 @@ 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 9d32a81ece08..7f4356c520be 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6212,15 +6212,18 @@ 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)) {
- /*
- * 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)) {
+ /*
+ * 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);
}
sd = rcu_dereference(per_cpu(sd_llc, target));
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ff23cd92d25f..3cb7de0b11d7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1014,6 +1014,8 @@ 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_SMP
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");
--
2.16.4
next prev parent reply other threads:[~2020-03-20 15:13 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-20 15:12 [PATCH 0/4] Throttle select_idle_sibling when a target domain is overloaded Mel Gorman
2020-03-20 15:12 ` [PATCH 1/4] sched/fair: Track efficiency of select_idle_sibling Mel Gorman
2020-03-23 13:30 ` Valentin Schneider
2020-03-23 13:55 ` Mel Gorman
2020-03-20 15:12 ` Mel Gorman [this message]
2020-03-23 13:30 ` [PATCH 2/4] sched/fair: Track efficiency of task recent_used_cpu Valentin Schneider
2020-03-20 15:12 ` [PATCH 3/4] sched/fair: Clear SMT siblings after determining the core is not idle Mel Gorman
2020-03-23 13:31 ` Valentin Schneider
2020-03-20 15:12 ` [PATCH 4/4] sched/fair: Track possibly overloaded domains and abort a scan if necessary Mel Gorman
2020-03-20 15:48 ` Vincent Guittot
2020-03-20 16:44 ` Mel Gorman
2020-03-20 16:54 ` Vincent Guittot
2020-03-20 17:43 ` Mel Gorman
2020-03-24 10:35 ` Vincent Guittot
2020-03-24 11:23 ` Mel Gorman
2020-04-02 7:59 ` [sched/fair] 15e7470dfc: hackbench.throughput 11.2% improvement kernel test robot
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