Re: [RFC PATCH] clocksource: increase watchdog retries

From: Paul E. McKenney
Date: Mon Nov 01 2021 - 20:10:07 EST


On Mon, Nov 01, 2021 at 11:28:03AM +0100, Jiri Wiesner wrote:
> On Thu, Oct 28, 2021 at 11:42:09AM -0700, Paul E. McKenney wrote:
> > On Thu, Oct 28, 2021 at 06:20:25PM +0200, Jiri Wiesner wrote:
> > > 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@xxxxxxxxxx>
> > > > 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.
> >
> > Very good, and thank you for giving it a go!
>
> Thank you for the fix! It resolves several strange results we got in our performance testing.
>
> > If it passes the upcoming tests
>
> I have done 300 reboots of the testing machine. Again, TSC was stable every time.
>
> > may I have your Tested-by?
>
> Absolutely:
> Tested-by: Jiri Wiesner <jwiesner@xxxxxxx>

Applied, thank you!

Thanx, Paul