From: Waiman Long <longman@redhat.com>
To: paulmck@kernel.org
Cc: John Stultz <john.stultz@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Stephen Boyd <sboyd@kernel.org>, Feng Tang <feng.tang@intel.com>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Cassio Neri <cassio.neri@gmail.com>,
Linus Walleij <linus.walleij@linaro.org>,
Frederic Weisbecker <frederic@kernel.org>
Subject: Re: [PATCH v2 0/4] clocksource: Avoid incorrect hpet fallback
Date: Wed, 17 Nov 2021 16:55:45 -0500 [thread overview]
Message-ID: <ede5405d-55f4-e1ea-23ef-56303cbfa411@redhat.com> (raw)
In-Reply-To: <20211117212547.GO641268@paulmck-ThinkPad-P17-Gen-1>
On 11/17/21 16:25, Paul E. McKenney wrote:
> On Wed, Nov 17, 2021 at 01:51:51PM -0500, Waiman Long wrote:
>> On 11/17/21 11:54, Paul E. McKenney wrote:
>>> On Tue, Nov 16, 2021 at 06:44:22PM -0500, Waiman Long wrote:
>>> A few questions:
>>>
>>> 1. Once you have all the patches in place, is the increase in
>>> WATCHDOG_MAX_SKEW from 50us to 100us necessary?
>> I think so. Using Feng's reproducer, I was able to cause a hpet-hpet delay
>> of more than 90us on a 1-socket system. With a default 50us
>> WATCHDOG_MAX_SKEW, the chance of a warning showing up will be much higher.
>> Trying to minimize the chance that a warning may appear is my primary reason
>> to increase WATCHDOG_MAX_SKEW.
> Should we downgrade the "had to retry read" complain to pr_info(),
> and make the only real warning be the case where a large number of
> consecutive read attempts fail? I believe that Heiner Kallweit was
> looking for something like this.
Sure. I will downgrade it to pr_info().
>
>>> 2. The reason for having cs->uncertainty_margin set to
>>> 2*WATCHDOG_MAX_SKEW was to allow for worst-case skew from both
>>> the previous and the current reading. Are you sure that
>>> dropping back to WATCHDOG_MAX_SKEW avoids false positives?
>> I can remove the hunk of changing cs->uncertainty_margin. It is critical for
>> this patch.
> Assuming "not critical", good!
Yes, it is "not critical". Somehow I missed the "not" :-)
Cheers,
Longman
prev parent reply other threads:[~2021-11-17 21:57 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-16 23:44 [PATCH v2 0/4] clocksource: Avoid incorrect hpet fallback Waiman Long
2021-11-16 23:44 ` [PATCH v2 1/4] clocksource: Avoid accidental unstable marking of clocksources Waiman Long
2021-11-16 23:44 ` [PATCH v2 2/4] clocksource: Reduce the default clocksource_watchdog() retries to 2 Waiman Long
2021-11-16 23:44 ` [PATCH v2 3/4] clocksource: Dynamically increase watchdog_max_skew Waiman Long
2021-11-16 23:44 ` [PATCH v2 4/4] clocksource: Add a Kconfig option for WATCHDOG_MAX_SKEW Waiman Long
2021-11-17 16:54 ` [PATCH v2 0/4] clocksource: Avoid incorrect hpet fallback Paul E. McKenney
2021-11-17 18:51 ` Waiman Long
2021-11-17 21:25 ` Paul E. McKenney
2021-11-17 21:55 ` Waiman Long [this message]
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