From: Waiman Long <longman@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Robert Richter <rrichter@marvell.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Mike Rapoport <rppt@linux.ibm.com>,
Kees Cook <keescook@chromium.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2] watchdog: Fix possible soft lockup warning at bootup
Date: Thu, 16 Jan 2020 12:34:09 -0500 [thread overview]
Message-ID: <9ae2ee4d-7b67-50ff-e736-1d51753c5ccd@redhat.com> (raw)
In-Reply-To: <87tv4vuyo6.fsf@nanos.tec.linutronix.de>
On 1/16/20 11:57 AM, Thomas Gleixner wrote:
>> So your theory the MONOTONIC clock runs differently/wrongly could
>> explain that (assuming this drives the sched clock). Though, I am
> No. sched_clock() is separate. It uses a raw timestamp (in your case
> from the ARM arch timer) and converts it to something which is close to
> proper time. So my assumption was based on the printout Waiman had:
>
> [ 1... ] CPU.... watchdog_fn now 170000000
> [ 25.. ] CPU.... watchdog_fn now 4170000000
>
> I assumed that now comes from ktime_get() or something like
> that. Waiman?
I printed out the now parameter of the __hrtimer_run_queues() call. So
from the timer perspective, it is losing time. For watchdog, the soft
expiry time is 4s. The watchdog function won't be called until the
timer's time advances 4s or more. That corresponds to about 24s in
timestamp time for that particular class of systems.
Cheers,
Longman
next prev parent reply other threads:[~2020-01-16 17:34 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-03 15:10 [PATCH v2] watchdog: Fix possible soft lockup warning at bootup Waiman Long
2020-01-16 2:06 ` Thomas Gleixner
2020-01-16 11:44 ` Thomas Gleixner
2020-01-16 15:11 ` Robert Richter
2020-01-16 16:57 ` Thomas Gleixner
2020-01-16 17:34 ` Waiman Long [this message]
2020-01-16 19:10 ` Thomas Gleixner
2020-01-16 19:13 ` Waiman Long
2020-01-16 18:17 ` [PATCH] watchdog/softlockup: Enforce that timestamp is valid on boot Thomas Gleixner
2020-01-17 10:25 ` [tip: core/core] " tip-bot2 for Thomas Gleixner
2020-01-16 15:34 ` [PATCH v2] watchdog: Fix possible soft lockup warning at bootup Waiman Long
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