From: Thomas Gleixner <tglx@linutronix.de>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org,
sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com,
maz@kernel.org, kernel-team@meta.com, neeraju@codeaurora.org,
ak@linux.intel.com, feng.tang@intel.com, zhengjun.xing@intel.com,
Waiman Long <longman@redhat.com>,
John Stultz <jstultz@google.com>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH clocksource 5/6] clocksource: Suspend the watchdog temporarily when high read latency detected
Date: Wed, 11 Jan 2023 12:26:58 +0100 [thread overview]
Message-ID: <87r0w1ia65.ffs@tglx> (raw)
In-Reply-To: <20230105010701.1773895-5-paulmck@kernel.org>
On Wed, Jan 04 2023 at 17:07, Paul E. McKenney wrote:
> This can be reproduced by running memory intensive 'stream' tests,
> or some of the stress-ng subcases such as 'ioport'.
>
> The reason for these issues is the when system is under heavy load, the
> read latency of the clocksources can be very high. Even lightweight TSC
> reads can show high latencies, and latencies are much worse for external
> clocksources such as HPET or the APIC PM timer. These latencies can
> result in false-positive clocksource-unstable determinations.
>
> Given that the clocksource watchdog is a continual diagnostic check with
> frequency of twice a second, there is no need to rush it when the system
> is under heavy load. Therefore, when high clocksource read latencies
> are detected, suspend the watchdog timer for 5 minutes.
We should have enough heuristics in place by now to qualify the output of
the clocksource watchdog as a random number generator, right?
next prev parent reply other threads:[~2023-01-11 11:40 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-05 1:04 [PATCH clocksource 0/6] Clocksource watchdog updates for v6.3 Paul E. McKenney
2023-01-05 1:06 ` [PATCH clocksource 1/6] clocksource: Print clocksource name when clocksource is tested unstable Paul E. McKenney
2023-01-05 1:06 ` [PATCH clocksource 2/6] clocksource: Loosen clocksource watchdog constraints Paul E. McKenney
2023-01-05 1:06 ` [PATCH clocksource 3/6] clocksource: Improve read-back-delay message Paul E. McKenney
2023-01-05 1:06 ` [PATCH clocksource 4/6] clocksource: Improve "skew is too large" messages Paul E. McKenney
2023-01-05 1:07 ` [PATCH clocksource 5/6] clocksource: Suspend the watchdog temporarily when high read latency detected Paul E. McKenney
2023-01-11 11:26 ` Thomas Gleixner [this message]
2023-01-11 12:31 ` Feng Tang
2023-01-11 17:50 ` Paul E. McKenney
2023-01-11 21:19 ` Thomas Gleixner
2023-01-11 21:32 ` Paul E. McKenney
2023-01-12 0:59 ` Feng Tang
2023-01-05 1:07 ` [PATCH clocksource 6/6] clocksource: Verify HPET and PMTMR when TSC unverified Paul E. McKenney
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