linux-kernel - Re: [PATCH v7 clocksource 5/5] clocksource: Do pairwise clock-desynchronization checking

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Message-ID: <878s5q4iix.ffs@nanos.tec.linutronix.de>
Date:   Sat, 10 Apr 2021 11:04:54 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     paulmck@...nel.org, linux-kernel@...r.kernel.org
Cc:     john.stultz@...aro.org, sboyd@...nel.org, corbet@....net,
        Mark.Rutland@....com, maz@...nel.org, kernel-team@...com,
        neeraju@...eaurora.org, ak@...ux.intel.com,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v7 clocksource 5/5] clocksource: Do pairwise clock-desynchronization checking

On Fri, Apr 02 2021 at 15:49, paulmck wrote:
> From: "Paul E. McKenney" <paulmck@...nel.org>
>
> Although smp_call_function() has the advantage of simplicity, using
> it to check for cross-CPU clock desynchronization means that any CPU
> being slow reduces the sensitivity of the checking across all CPUs.
> And it is not uncommon for smp_call_function() latencies to be in the
> hundreds of microseconds.
>
> This commit therefore switches to smp_call_function_single(), so that
> delays from a given CPU affect only those measurements involving that
> particular CPU.

Is there any reason I'm missing why this is not done right in patch 3/5
which introduces this synchronization check?

Thanks,

        tglx