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 04/10] sched/fair: Return an idle cpu if one is found after a failed search for an idle core
Date: Thu, 3 Dec 2020 14:11:18 +0000 [thread overview]
Message-ID: <20201203141124.7391-5-mgorman@techsingularity.net> (raw)
In-Reply-To: <20201203141124.7391-1-mgorman@techsingularity.net>
select_idle_core is called when SMT is active and there is likely a free
core available. It may find idle CPUs but this information is simply
discarded and the scan starts over again with select_idle_cpu.
This patch caches information on idle CPUs found during the search for
a core and uses one if no core is found. This is a tradeoff. There may
be a slight impact when utilisation is low and an idle core can be
found quickly. It provides improvements as the number of busy CPUs
approaches 50% of the domain size when SMT is enabled.
With tbench on a 2-socket CascadeLake machine, 80 logical CPUs, HT enabled
5.10.0-rc6 5.10.0-rc6
schedstat idlecandidate
Hmean 1 500.06 ( 0.00%) 505.67 * 1.12%*
Hmean 2 975.90 ( 0.00%) 974.06 * -0.19%*
Hmean 4 1902.95 ( 0.00%) 1904.43 * 0.08%*
Hmean 8 3761.73 ( 0.00%) 3721.02 * -1.08%*
Hmean 16 6713.93 ( 0.00%) 6769.17 * 0.82%*
Hmean 32 10435.31 ( 0.00%) 10312.58 * -1.18%*
Hmean 64 12325.51 ( 0.00%) 13792.01 * 11.90%*
Hmean 128 21225.21 ( 0.00%) 20963.44 * -1.23%*
Hmean 256 20532.83 ( 0.00%) 20335.62 * -0.96%*
Hmean 320 20334.81 ( 0.00%) 20147.25 * -0.92%*
In this particular test, the cost/benefit is marginal except
for 64 which was a point where the machine was over 50% busy
but not fully utilised.
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
kernel/sched/fair.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fc48cc99b03d..845bc0cd9158 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6066,6 +6066,7 @@ void __update_idle_core(struct rq *rq)
*/
static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
{
+ int idle_candidate = -1;
struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
int core, cpu;
@@ -6084,7 +6085,13 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
schedstat_inc(this_rq()->sis_scanned);
if (!available_idle_cpu(cpu)) {
idle = false;
- break;
+ if (idle_candidate != -1)
+ break;
+ }
+
+ if (idle_candidate == -1 &&
+ cpumask_test_cpu(cpu, p->cpus_ptr)) {
+ idle_candidate = cpu;
}
}
@@ -6099,7 +6106,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
*/
set_idle_cores(target, 0);
- return -1;
+ return idle_candidate;
}
/*
--
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 ` [PATCH 02/10] sched/fair: Track efficiency of task recent_used_cpu Mel Gorman
2020-12-03 14:11 ` [PATCH 03/10] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2020-12-03 14:11 ` Mel Gorman [this message]
2020-12-03 16:35 ` [PATCH 04/10] sched/fair: Return an idle cpu if one is found after a failed search for an idle core 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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