From: Peter Zijlstra <peterz@infradead.org>
To: Balbir Singh <bsingharora@gmail.com>
Cc: tglx@linutronix.de, mingo@kernel.org, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
bristot@redhat.com, pbonzini@redhat.com, maz@kernel.org,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
riel@surriel.com, hannes@cmpxchg.org
Subject: Re: [PATCH 0/6] sched,delayacct: Some cleanups
Date: Thu, 6 May 2021 11:13:52 +0200 [thread overview]
Message-ID: <YJOzUAg30LZWSHcI@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210505222940.GA4236@balbir-desktop>
On Thu, May 06, 2021 at 08:29:40AM +1000, Balbir Singh wrote:
> On Wed, May 05, 2021 at 12:59:40PM +0200, Peter Zijlstra wrote:
> > Hi,
> >
> > Due to:
> >
> > https://lkml.kernel.org/r/0000000000001d43ac05c0f5c6a0@google.com
> >
> > and general principle, delayacct really shouldn't be using ktime (pvclock also
> > really shouldn't be doing what it does, but that's another story). This lead me
> > to looking at the SCHED_INFO, SCHEDSTATS, DELAYACCT (and PSI) accounting hell.
> >
> > The rest of the patches are an attempt at simplifying all that a little. All
> > that crud is enabled by default for distros which is leading to a death by a
> > thousand cuts.
> >
> > The last patch is an attempt at default disabling DELAYACCT, because I don't
> > think anybody actually uses that much, but what do I know, there were no ill
> > effects on my testbox. Perhaps we should mirror
> > /proc/sys/kernel/sched_schedstats and provide a delayacct sysctl for runtime
> > frobbing.
> >
>
> There are tools like iotop that use delayacct to display information.
Right, but how many actual people use that? Does that justify saddling
the whole sodding world with the overhead?
> When the
> code was checked in, we did run SPEC* back in the day 2006 to find overheads,
> nothing significant showed. Do we have any date on the overhead your seeing?
I've not looked, but having it disabled saves that per-task allocation
and that spinlock in delayacct_end() for iowait wakeups and a bunch of
cache misses ofcourse.
I doubt SPEC is a benchmark that tickles those paths much if at all.
The thing is; we can't just keep growing more and more stats, that'll
kill us quite dead.
next prev parent reply other threads:[~2021-05-06 9:16 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-05 10:59 [PATCH 0/6] sched,delayacct: Some cleanups Peter Zijlstra
2021-05-05 10:59 ` [PATCH 1/6] delayacct: Use sched_clock() Peter Zijlstra
2021-05-05 14:40 ` Rik van Riel
2021-05-06 13:59 ` Johannes Weiner
2021-05-06 14:17 ` Peter Zijlstra
2021-05-06 15:17 ` Johannes Weiner
2021-05-07 12:40 ` Balbir Singh
2021-05-12 10:43 ` Mel Gorman
2021-05-05 10:59 ` [PATCH 2/6] sched: Rename sched_info_{queued,dequeued} Peter Zijlstra
2021-05-05 14:39 ` Rik van Riel
2021-05-06 13:59 ` Johannes Weiner
2021-05-10 8:45 ` Balbir Singh
2021-05-12 10:49 ` Mel Gorman
2021-05-05 10:59 ` [PATCH 3/6] sched: Simplify sched_info_on() Peter Zijlstra
2021-05-06 14:03 ` Johannes Weiner
2021-05-12 11:10 ` Mel Gorman
2021-05-12 11:32 ` Peter Zijlstra
2021-05-12 12:51 ` Mel Gorman
2021-05-05 10:59 ` [PATCH 4/6] kvm: Select SCHED_INFO instead of TASK_DELAY_ACCT Peter Zijlstra
2021-05-05 11:37 ` Paolo Bonzini
2021-05-06 14:38 ` Marc Zyngier
2021-05-07 12:42 ` Balbir Singh
2021-05-12 11:11 ` Mel Gorman
2021-05-05 10:59 ` [PATCH 5/6] delayacct: Add static_branch in scheduler hooks Peter Zijlstra
2021-05-06 14:05 ` Johannes Weiner
2021-05-10 8:42 ` Balbir Singh
2021-05-12 11:13 ` Mel Gorman
2021-05-05 10:59 ` [PATCH 6/6] [RFC] delayacct: Default disabled Peter Zijlstra
2021-05-12 11:35 ` Mel Gorman
2021-05-05 22:29 ` [PATCH 0/6] sched,delayacct: Some cleanups Balbir Singh
2021-05-06 9:13 ` Peter Zijlstra [this message]
2021-05-07 12:38 ` Balbir Singh
2021-05-12 11:34 ` Mel Gorman
2021-05-12 11:38 ` Peter Zijlstra
2021-05-12 12:23 ` Paul Wise
2021-05-12 13:00 ` Mel Gorman
2021-05-13 1:29 ` Paul Wise
2021-06-25 0:50 ` Paul Wise
2021-05-07 9:05 ` Thomas Gleixner
2021-05-10 7:08 ` Ingo Molnar
2021-05-10 12:05 ` [PATCH 7/6] delayacct: Add sysctl to enable at runtime Peter Zijlstra
2021-05-10 12:06 ` Peter Zijlstra
2021-05-12 11:40 ` Mel Gorman
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