linux-kernel - Re: clocksource: Reduce watchdog readout delay limit to prevent false positives

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Message-ID: <9cad0f11-97f1-42f2-bc26-210701350690@paulmck-laptop>
Date: Sat, 20 Dec 2025 08:39:30 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Daniel J Blueman <daniel@...ra.org>,
	John Stultz <jstultz@...gle.com>, Waiman Long <longman@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Tony Luck <tony.luck@...el.com>, Borislav Petkov <bp@...en8.de>,
	Stephen Boyd <sboyd@...nel.org>,
	Scott Hamilton <scott.hamilton@...den.com>
Subject: Re: clocksource: Reduce watchdog readout delay limit to prevent
 false positives

On Sat, Dec 20, 2025 at 09:37:40AM +0100, Thomas Gleixner wrote:
> On Fri, Dec 19 2025 at 16:18, Paul E. McKenney wrote:
> > On Fri, Dec 19, 2025 at 11:13:05AM +0100, Thomas Gleixner wrote:
> >> > My concern is that the patch below would force needless cs_watchdog_read()
> >> > retries.
> >> 
> >> That's not the end of the world and way better than degrading the
> >> watchdog further.
> >
> > But what you proposed is just a further tweak of the heuristics you so
> > energetically decry above.
> 
> I fully agree that it is a bandaid fix, but it makes the machinery
> consistent and correct. It prevents false positives, which are
> inevitable in the current design. No?

It might also be necessary to compensate by tweaking up the number of
retries by adjusting clocksource_get_max_watchdog_retry().

							Thanx, Paul