From: Thomas Gleixner <tglx@linutronix.de>
To: Andi Kleen <ak@linux.intel.com>, "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@fb.com, neeraju@codeaurora.org,
feng.tang@intel.com, zhengjun.xing@intel.com,
Chris Mason <clm@fb.com>
Subject: Re: [PATCH v10 clocksource 3/7] clocksource: Check per-CPU clock synchronization when marked unstable
Date: Mon, 26 Apr 2021 09:16:59 +0200 [thread overview]
Message-ID: <871raxv7kk.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210426041235.GT1401198@tassilo.jf.intel.com>
On Sun, Apr 25 2021 at 21:12, Andi Kleen wrote:
> On Sun, Apr 25, 2021 at 03:47:04PM -0700, Paul E. McKenney wrote:
>> Some sorts of per-CPU clock sources have a history of going out of
>> synchronization with each other. However, this problem has purportedy
>> been solved in the past ten years. Except that it is all too possible
>> that the problem has instead simply been made less likely, which might
>> mean that some of the occasional "Marking clocksource 'tsc' as unstable"
>> messages might be due to desynchronization. How would anyone know?
>>
>> Therefore apply CPU-to-CPU synchronization checking to newly unstable
>> clocksource that are marked with the new CLOCK_SOURCE_VERIFY_PERCPU flag.
>> Lists of desynchronized CPUs are printed, with the caveat that if it
>> is the reporting CPU that is itself desynchronized, it will appear that
>> all the other clocks are wrong. Just like in real life.
>
> Well I could see this causing a gigantic flood of messages then.
> Assume I have 300 cores, do I get all those messages 300 times repeated
> then? If the console is slow this might end up taking a lot
> of CPU time.
Exactly 4 pr_warn() lines in dmesg which are emitted exactly once when
the TSC deviates from the watchdog where three of them print a cpumask
are really a gigantic flood of messsages.
Thanks,
tglx
next prev parent reply other threads:[~2021-04-26 7:17 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-25 22:45 [PATCH v10 clocksource 0/7] Do not mark clocks unstable due to delays for v5.13 Paul E. McKenney
2021-04-25 22:47 ` [PATCH v10 clocksource 1/7] clocksource: Provide module parameters to inject delays in watchdog Paul E. McKenney
2021-04-26 4:07 ` Andi Kleen
2021-04-26 7:13 ` Thomas Gleixner
2021-04-26 15:28 ` Paul E. McKenney
2021-04-26 16:00 ` Andi Kleen
2021-04-26 16:14 ` Paul E. McKenney
2021-04-26 17:56 ` Andi Kleen
2021-04-26 18:24 ` Paul E. McKenney
2021-04-28 4:49 ` Luming Yu
2021-04-28 13:57 ` Paul E. McKenney
2021-04-28 14:24 ` Luming Yu
2021-04-28 14:37 ` Thomas Gleixner
2021-04-25 22:47 ` [PATCH v10 clocksource 2/7] clocksource: Retry clock read if long delays detected Paul E. McKenney
2021-04-27 1:44 ` Feng Tang
2021-04-25 22:47 ` [PATCH v10 clocksource 3/7] clocksource: Check per-CPU clock synchronization when marked unstable Paul E. McKenney
2021-04-26 4:12 ` Andi Kleen
2021-04-26 7:16 ` Thomas Gleixner [this message]
2021-04-25 22:47 ` [PATCH v10 clocksource 4/7] clocksource: Provide a module parameter to fuzz per-CPU clock checking Paul E. McKenney
2021-04-25 22:47 ` [PATCH v10 clocksource 5/7] clocksource: Limit number of CPUs checked for clock synchronization Paul E. McKenney
2021-04-25 22:47 ` [PATCH v10 clocksource 6/7] clocksource: Forgive tsc_early pre-calibration drift Paul E. McKenney
2021-04-26 15:01 ` Feng Tang
2021-04-26 15:25 ` Paul E. McKenney
2021-04-26 15:36 ` Feng Tang
2021-04-26 18:26 ` Paul E. McKenney
2021-04-27 1:13 ` Feng Tang
2021-04-27 3:46 ` Paul E. McKenney
2021-04-27 4:16 ` Feng Tang
2021-04-26 15:28 ` Thomas Gleixner
2021-04-27 21:03 ` Thomas Gleixner
2021-04-27 7:27 ` [clocksource] 8c30ace35d: WARNING:at_kernel/time/clocksource.c:#clocksource_watchdog kernel test robot
2021-04-27 8:45 ` Feng Tang
2021-04-27 13:37 ` Paul E. McKenney
2021-04-27 17:50 ` Paul E. McKenney
2021-04-27 21:09 ` Thomas Gleixner
2021-04-28 1:48 ` Paul E. McKenney
2021-04-28 10:14 ` Thomas Gleixner
2021-04-28 18:31 ` Paul E. McKenney
2021-04-28 13:34 ` Thomas Gleixner
2021-04-28 15:39 ` Peter Zijlstra
2021-04-28 17:00 ` Thomas Gleixner
2021-04-29 7:38 ` Feng Tang
2021-04-28 18:31 ` Paul E. McKenney
2021-04-29 8:27 ` Thomas Gleixner
2021-04-29 14:26 ` Paul E. McKenney
2021-04-29 17:30 ` Thomas Gleixner
2021-04-29 23:04 ` Andi Kleen
2021-04-30 0:24 ` Paul E. McKenney
2021-04-30 0:59 ` Paul E. McKenney
2021-04-30 5:08 ` Paul E. McKenney
2021-04-25 22:47 ` [PATCH v9 clocksource 6/6] clocksource: Reduce WATCHDOG_THRESHOLD Paul E. McKenney
2021-04-25 22:47 ` [PATCH v10 clocksource 7/7] " Paul E. McKenney
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