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Message-ID: <Y85MNmZDc5czMRUJ@dhcp22.suse.cz>
Date: Mon, 23 Jan 2023 09:58:30 +0100
From: Michal Hocko <mhocko@...e.com>
To: Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc: Vlastimil Babka <vbabka@...e.cz>,
Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Ingo Molnar <mingo@...hat.com>,
Johannes Weiner <hannes@...xchg.org>,
Shakeel Butt <shakeelb@...gle.com>,
Muchun Song <muchun.song@...ux.dev>,
Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...hsingularity.net>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH mm-unstable] lib/Kconfig.debug: do not enable
DEBUG_PREEMPT by default
On Sat 21-01-23 20:54:15, Hyeonggon Yoo wrote:
> On Sat, Jan 21, 2023 at 12:29:44PM +0100, Vlastimil Babka wrote:
> > On 1/21/23 04:39, Hyeonggon Yoo wrote:
> > > In workloads where this_cpu operations are frequently performed,
> > > enabling DEBUG_PREEMPT may result in significant increase in
> > > runtime overhead due to frequent invocation of
> > > __this_cpu_preempt_check() function.
> > >
> > > This can be demonstrated through benchmarks such as hackbench where this
> > > configuration results in a 10% reduction in performance, primarily due to
> > > the added overhead within memcg charging path.
> > >
> > > Therefore, do not to enable DEBUG_PREEMPT by default and make users aware
> > > of its potential impact on performance in some workloads.
> > >
> > > hackbench-process-sockets
> > > debug_preempt no_debug_preempt
> > > Amean 1 0.4743 ( 0.00%) 0.4295 * 9.45%*
> > > Amean 4 1.4191 ( 0.00%) 1.2650 * 10.86%*
> > > Amean 7 2.2677 ( 0.00%) 2.0094 * 11.39%*
> > > Amean 12 3.6821 ( 0.00%) 3.2115 * 12.78%*
> > > Amean 21 6.6752 ( 0.00%) 5.7956 * 13.18%*
> > > Amean 30 9.6646 ( 0.00%) 8.5197 * 11.85%*
> > > Amean 48 15.3363 ( 0.00%) 13.5559 * 11.61%*
> > > Amean 79 24.8603 ( 0.00%) 22.0597 * 11.27%*
> > > Amean 96 30.1240 ( 0.00%) 26.8073 * 11.01%*
Do you happen to have any perf data collected during those runs? I
would be interested in the memcg side of things. Maybe we can do
something better there.
--
Michal Hocko
SUSE Labs
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