From: Peter Zijlstra <peterz@infradead.org>
To: Xi Wang <xii@google.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
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, Paul Turner <pjt@google.com>
Subject: Re: [PATCH v2 1/1] sched: watchdog: Touch kernel watchdog with sched count
Date: Wed, 21 Oct 2020 11:59:51 +0200 [thread overview]
Message-ID: <20201021095951.GB2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201020205704.1741543-2-xii@google.com>
On Tue, Oct 20, 2020 at 01:57:04PM -0700, 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 / jitter
> from periodically invoking watchdog reset in thread context, we can
> simply test if pick_next_task can run. This is done by forcing resched
> and checking rq->sched_count.
Whitespace exists for a reason, use more of it. Also, the above isn't
actually accurate anymore and carried over from the previous
implementation.
> 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. These steps are unlikely to silently fail. The
> change would provide nearly the same level of protection with less
> overhead.
>
> With this patch we can still switch back to the old method with the
> boot option watchdog_touch_with_thread. However code for the old
> method can be completely removed in the future.
I'd suggest removing all the #ifdef and config muck. Either its a good
idea or it's not.
next prev parent reply other threads:[~2020-10-21 10:00 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-20 20:57 [PATCH v2 0/1] " Xi Wang
2020-10-20 20:57 ` [PATCH v2 1/1] sched: watchdog: " Xi Wang
2020-10-21 9:59 ` Peter Zijlstra [this message]
2020-10-21 10:12 ` Peter Zijlstra
2020-10-21 10:24 ` Peter Zijlstra
2020-10-21 11:11 ` Peter Zijlstra
2020-10-21 23:48 ` Xi Wang
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