From: Peter Zijlstra <peterz@infradead.org>
To: Xi Wang <xii@google.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Josh Don <joshdon@google.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Paul Turner <pjt@google.com>
Subject: Re: [PATCH] sched: watchdog: Touch kernel watchdog in sched code
Date: Thu, 5 Mar 2020 08:57:42 +0100 [thread overview]
Message-ID: <20200305075742.GR2596@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200304213941.112303-1-xii@google.com>
On Wed, Mar 04, 2020 at 01:39:41PM -0800, Xi Wang wrote:
> The main purpose of kernel watchdog is to test whether scheduler can
> still schedule tasks on a cpu. In order to reduce latency from
> periodically invoking watchdog reset in thread context, we can simply
> touch watchdog from pick_next_task in scheduler. Compared to actually
> resetting watchdog from cpu stop / migration threads, we lose coverage
> on: a migration thread actually get picked and we actually context
> switch to the migration thread. Both steps are heavily protected by
> kernel locks and unlikely to silently fail. Thus the change would
> provide the same level of protection with less overhead.
>
> The new way vs the old way to touch the watchdogs is configurable
> from:
>
> /proc/sys/kernel/watchdog_touch_in_thread_interval
>
> The value means:
> 0: Always touch watchdog from pick_next_task
> 1: Always touch watchdog from migration thread
> N (N>0): Touch watchdog from migration thread once in every N
> invocations, and touch watchdog from pick_next_task for
> other invocations.
>
This is configurable madness. What are we really trying to do here?
next prev parent reply other threads:[~2020-03-05 7:57 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-04 21:39 [PATCH] sched: watchdog: Touch kernel watchdog in sched code Xi Wang
2020-03-05 3:11 ` Steven Rostedt
2020-03-05 7:57 ` Peter Zijlstra [this message]
2020-03-05 18:07 ` Thomas Gleixner
2020-03-05 21:41 ` Xi Wang
2020-03-05 22:07 ` Paul Turner
[not found] ` <CAOBoifgHNag0P33PKg81iNoCjxenJHfBZG-t-8aEkr_Tjf7o_w@mail.gmail.com>
2020-03-06 8:28 ` Peter Zijlstra
2020-03-05 22:11 ` Paul Turner
2020-03-06 8:40 ` Peter Zijlstra
2020-03-06 22:34 ` Xi Wang
2020-10-05 11:19 ` Peter Zijlstra
2020-10-06 2:21 ` Xi Wang
2020-03-10 8:43 ` [sched] db8e976e4a: will-it-scale.per_process_ops 15.8% improvement kernel test robot
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