netdev - Re: [PATCH] igb: shorten maximum PHC timecounter update interval

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Message-ID: <20181026120416.GB27139@localhost>
Date:   Fri, 26 Oct 2018 14:04:16 +0200
From:   Miroslav Lichvar <mlichvar@...hat.com>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
        Jacob Keller <jacob.e.keller@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] igb: shorten maximum PHC timecounter update interval

On Fri, Oct 12, 2018 at 07:05:30AM -0700, Richard Cochran wrote:
> On Fri, Oct 12, 2018 at 01:13:39PM +0200, Miroslav Lichvar wrote:
> > Since commit 500462a9d ("timers: Switch to a non-cascading wheel"),
> > scheduling of delayed work seems to be less accurate and a requested
> > delay of 540 seconds may actually be longer than 550 seconds. Shorten
> > the delay to 480 seconds to be sure the timecounter is updated in time.
> 
> Good catch.  This timer wheel change will affect other, similar
> drivers.  Guess I'll go through and adjust their timeouts, too.

I just realized that we need to fit there also any frequency
adjustments of the PHC and system clock. The PHC can be set to run up
to 6% faster and the system clock can be slowed down by up to 10%.

Those 480 seconds in the igb driver is not short enough for that.
Should I fix and resend this patch, or send a new one?

Other drivers may have a similar problem.

-- 
Miroslav Lichvar