linux-kernel - [RFC PATCH v2 0/1] Reduce cost of accessing tg->load

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Message-ID: <20230816024831.682107-1-aaron.lu@intel.com>
Date:   Wed, 16 Aug 2023 10:48:30 +0800
From:   Aaron Lu <aaron.lu@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Tim Chen <tim.c.chen@...el.com>,
        Nitin Tekchandani <nitin.tekchandani@...el.com>,
        Yu Chen <yu.c.chen@...el.com>,
        Waiman Long <longman@...hat.com>,
        Deng Pan <pan.deng@...el.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH v2 0/1] Reduce cost of accessing tg->load_avg

Nitin Tekchandani noticed some scheduler functions have high cost
according to perf/cycles while running postgres_sysbench workload.
I perf/annotated the high cost functions: update_cfs_group() and
update_load_avg() and found the costs were ~90% due to accessing to
tg->load_avg. This series is an attempt to reduce the overhead of
the two functions.

Thanks to Vincent's suggestion from v1, this revision used a simpler way
to solve the overhead problem by limiting updates to tg->load_avg to at
most once per ms. Benchmark shows that it has good results and with the
rate limit in place, other optimizations in v1 don't improve performance
further so they are dropped from this revision.

Aaron Lu (1):
  sched/fair: ratelimit update to tg->load_avg

 kernel/sched/fair.c  | 13 ++++++++++++-
 kernel/sched/sched.h |  1 +
 2 files changed, 13 insertions(+), 1 deletion(-)

-- 
2.41.0