From: Peter Zijlstra <peterz@infradead.org>
To: Petr Mladek <pmladek@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
Laurence Oberman <loberman@redhat.com>,
Vincent Whitchurch <vincent.whitchurch@axis.com>,
Michal Hocko <mhocko@suse.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] watchdog/softlockup: Preserve original timestamp when touching watchdog externally
Date: Mon, 21 Oct 2019 14:42:14 +0200 [thread overview]
Message-ID: <20191021124214.GD1817@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190819104732.20966-2-pmladek@suse.com>
On Mon, Aug 19, 2019 at 12:47:30PM +0200, Petr Mladek wrote:
> Some bug report included the same softlockups in flush_tlb_kernel_range()
> in regular intervals. Unfortunately was not clear if there was a progress
> or not.
>
> The situation can be simulated with a simply busy loop:
>
> while (true)
> cpu_relax();
>
> The softlockup detector produces:
>
> [ 168.277520] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865]
> [ 196.277604] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865]
> [ 236.277522] watchdog: BUG: soft lockup - CPU#1 stuck for 23s! [cat:4865]
>
> One would expect only one softlockup report or several reports with
> an increased duration.
Let's just say our expectations differ.
> The result is that each softlockup is reported only once unless
> another process get scheduled:
>
> [ 320.248948] watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [cat:4916]
Which would greatly confuse me; as the above would have me think the
situation got resolved (no more lockups reported) even though it is
still very much stuck there.
IOW, I don't see how this makes anything better. You're removing
information.
next prev parent reply other threads:[~2019-10-21 12:42 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 10:47 [PATCH 0/3] watchdog/softlockup: Make softlockup reports more reliable and useful Petr Mladek
2019-08-19 10:47 ` [PATCH 1/3] watchdog/softlockup: Preserve original timestamp when touching watchdog externally Petr Mladek
2019-10-21 12:42 ` Peter Zijlstra [this message]
2019-10-21 13:04 ` Petr Mladek
2019-08-19 10:47 ` [PATCH 2/3] watchdog/softlockup: Report the same softlockup regularly Petr Mladek
2019-10-21 12:43 ` Peter Zijlstra
2019-10-21 13:40 ` Petr Mladek
2019-10-21 14:09 ` Peter Zijlstra
2019-08-19 10:47 ` [PATCH 3/3] Test softlockup Petr Mladek
2019-10-21 12:45 ` Peter Zijlstra
2019-10-21 13:06 ` Petr Mladek
2019-10-21 12:32 ` [PATCH 0/3] watchdog/softlockup: Make softlockup reports more reliable and useful Petr Mladek
-- strict thread matches above, loose matches on Subject: below --
2019-06-05 14:09 [RFC " Petr Mladek
2019-06-05 14:09 ` [PATCH 1/3] watchdog/softlockup: Preserve original timestamp when touching watchdog externally Petr Mladek
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