linux-kernel - Re: [PATCH 2/3 v3] time: Fix CLOCK_MONOTONIC

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Message-ID: <20170613103026.GF4221@localhost>
Date:   Tue, 13 Jun 2017 12:30:26 +0200
From:   Miroslav Lichvar <mlichvar@...hat.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Richard Cochran <richardcochran@...il.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Stephen Boyd <stephen.boyd@...aro.org>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Will Deacon <will.deacon@....com>,
        Daniel Mentz <danielmentz@...gle.com>,
        "stable #4 . 8+" <stable@...r.kernel.org>
Subject: Re: [PATCH 2/3 v3] time: Fix CLOCK_MONOTONIC_RAW sub-nanosecond
 accounting

On Thu, Jun 08, 2017 at 04:44:21PM -0700, John Stultz wrote:
> Due to how the MONOTONIC_RAW accumulation logic was handled,
> there is the potential for a 1ns discontinuity when we do
> accumulations. This small discontinuity has for the most part
> gone un-noticed, but since ARM64 enabled CLOCK_MONOTONIC_RAW
> in their vDSO clock_gettime implementation, we've seen failures
> with the inconsistency-check test in kselftest.
> 
> This patch addresses the issue by using the same sub-ns
> accumulation handling that CLOCK_MONOTONIC uses, which avoids
> the issue for in-kernel users.

The patch looks good to me and in testing on x86_64 I didn't see any
issues with the CLOCK_MONOTONIC_RAW clock.

Thanks,

-- 
Miroslav Lichvar