linux-kernel - Re: [RFC PATCH] clocksource: increase watchdog retries

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Date:   Thu, 28 Oct 2021 18:20:25 +0200
From:   Jiri Wiesner <jwiesner@...e.de>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Mel Gorman <mgorman@...e.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Net <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH] clocksource: increase watchdog retries

On Wed, Oct 27, 2021 at 02:38:29PM -0700, Paul E. McKenney wrote:
> I had something like this pending, but people came up with other workloads
> that resulted in repeated delays.  In those cases, it does not make sense
> to ever mark the affected clocksource unstable.  This led me to the patch
> shown below, which splats after about 100 consecutive long-delay retries,
> but which avoids marking the clocksource unstable.  This is queued on -rcu.
> 
> Does this work for you?
> 
> commit 9ec2a03bbf4bee3d9fbc02a402dee36efafc5a2d
> Author: Paul E. McKenney <paulmck@...nel.org>
> Date:   Thu May 27 11:03:28 2021 -0700
> 
>     clocksource: Forgive repeated long-latency watchdog clocksource reads

Yes, it does. I have done 100 reboots of the testing machine (running 5.15-rc5 with the above patch applied) and TSC was stable every time. I am going to start a longer test of 300 reboots for good measure and report back next week. J.