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From: Vincent Guittot <vincent.guittot@linaro.org>
To: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
	dietmar.eggemann@arm.com, rostedt@goodmis.org,
	bsegall@google.com, mgorman@suse.de,
	linux-kernel@vger.kernel.org
Cc: valentin.schneider@arm.com, pauld@redhat.com, hdanton@sina.com,
	Vincent Guittot <vincent.guittot@linaro.org>
Subject: [PATCH 2/4 v2] sched/fair: reduce minimal imbalance threshold
Date: Mon, 21 Sep 2020 09:24:22 +0200	[thread overview]
Message-ID: <20200921072424.14813-3-vincent.guittot@linaro.org> (raw)
In-Reply-To: <20200921072424.14813-1-vincent.guittot@linaro.org>

The 25% default imbalance threshold for DIE and NUMA domain is large
enough to generate significant unfairness between threads. A typical
example is the case of 11 threads running on 2x4 CPUs. The imbalance of
20% between the 2 groups of 4 cores is just low enough to not trigger
the load balance between the 2 groups. We will have always the same 6
threads on one group of 4 CPUs and the other 5 threads on the other
group of CPUS. With a fair time sharing in each group, we ends up with
+20% running time for the group of 5 threads.

Consider decreasing the imbalance threshold for overloaded case where we
use the load to balance task and to ensure fair time sharing.

Acked-by: Hillf Danton <hdanton@sina.com>
Reviewed-by: Phil Auld <pauld@redhat.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/topology.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 249bec7b0a4c..41df62884cea 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1349,7 +1349,7 @@ sd_init(struct sched_domain_topology_level *tl,
 		.min_interval		= sd_weight,
 		.max_interval		= 2*sd_weight,
 		.busy_factor		= 32,
-		.imbalance_pct		= 125,
+		.imbalance_pct		= 117,
 
 		.cache_nice_tries	= 0,
 
-- 
2.17.1


  parent reply	other threads:[~2020-09-21  7:24 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-21  7:24 [PATCH 0/4 v2] sched/fair: Improve fairness between cfs tasks Vincent Guittot
2020-09-21  7:24 ` [PATCH 1/4 v2] sched/fair: relax constraint on task's load during load balance Vincent Guittot
2020-09-23 14:43   ` Valentin Schneider
2020-09-29  7:56   ` [tip: sched/core] sched/fair: Relax " tip-bot2 for Vincent Guittot
2020-09-21  7:24 ` Vincent Guittot [this message]
2020-09-23 14:43   ` [PATCH 2/4 v2] sched/fair: reduce minimal imbalance threshold Valentin Schneider
2020-09-29  7:56   ` [tip: sched/core] sched/fair: Reduce " tip-bot2 for Vincent Guittot
2020-09-21  7:24 ` [PATCH 3/4 v2] sched/fair: minimize concurrent LBs between domain level Vincent Guittot
2020-09-23 14:43   ` Valentin Schneider
2020-09-29  7:56   ` [tip: sched/core] sched/fair: Minimize " tip-bot2 for Vincent Guittot
2020-09-21  7:24 ` [PATCH 4/4 v2] sched/fair: reduce busy load balance interval Vincent Guittot
2020-09-23 14:43   ` Valentin Schneider
2020-09-29  7:56   ` [tip: sched/core] sched/fair: Reduce " tip-bot2 for Vincent Guittot
2020-09-23 15:47 ` [PATCH 0/4 v2] sched/fair: Improve fairness between cfs tasks Mel Gorman

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