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From: Thomas Gleixner <tglx@linutronix.de>
To: brookxu <brookxu.cn@gmail.com>, john.stultz@linaro.org, sboyd@kernel.org
Cc: linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] clocksource: skip check while watchdog hung up or unstable
Date: Wed, 11 Aug 2021 14:44:26 +0200	[thread overview]
Message-ID: <877dgsp2vp.ffs@tglx> (raw)
In-Reply-To: <63064a758eb087febce3eff5b2c736a5449b3dd2.1628675461.git.brookxu@tencent.com>

On Wed, Aug 11 2021 at 17:55, brookxu wrote:
> From: Chunguang Xu <brookxu@tencent.com>
>
> After patch 1f45f1f3 (clocksource: Make clocksource validation work
> for all clocksources), md_nsec may be 0 in some scenarios, such as
> the watchdog is delayed for a long time or the watchdog has a
> time-warp.

Maybe 0? There is exactly one single possibility for it to be zero:

  cs->wd_last == wdnow, i.e. delta = 0 -> wd_nsec = 0

So how does that condition solve any long delay or wrap around of the
watchdog? It's more than unlikely to hit exactly this case where the
readout is identical to the previous readout unless the watchdog stopped
counting.

> We found a problem when testing nvme disks with fio, when multiple
> queue interrupts of a disk were mapped to a single CPU. IO interrupt
> processing will cause the watchdog to be delayed for a long time
> (155 seconds), the system reports TSC unstable and switches the clock

If you hold off the softirq from running for 155 seconds then the TSC
watchdog is the least of your problems.

Thanks,

        tglx

  reply	other threads:[~2021-08-11 12:44 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-11  9:55 brookxu
2021-08-11 12:44 ` Thomas Gleixner [this message]
2021-08-11 13:18   ` brookxu
2021-08-11 14:01     ` Thomas Gleixner
2021-08-11 15:26       ` brookxu
2021-08-12 10:53         ` Thomas Gleixner
2021-08-13  0:54           ` brookxu

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