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

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Message-ID: <20210411002146.GW4510@paulmck-ThinkPad-P17-Gen-1>
Date:   Sat, 10 Apr 2021 17:21:46 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, 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
Subject: Re: [PATCH v7 clocksource 5/5] clocksource: Do pairwise
 clock-desynchronization checking

On Sat, Apr 10, 2021 at 11:04:54AM +0200, Thomas Gleixner wrote:
> 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?

None at all.  I will merge this into 3/5.

							Thanx, Paul