linux-kernel - Re: Extreme time jitter with suspend/resume cycles

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Date:   Thu, 5 Oct 2017 14:12:57 -0700
From:   Gabriel Beddingfield <gabe@...tlabs.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        John Stultz <john.stultz@...aro.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        linux-rtc@...r.kernel.org, Guy Erb <guy@...tlabs.com>,
        Howard Harte <hharte@...tlabs.com>
Subject: Re: Extreme time jitter with suspend/resume cycles

On Thu, Oct 5, 2017 at 2:04 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
>> > So that clocksource driver looks correct. Do you have an idea in which
>> > context this time jump happens? Does it happen when you exercise your high
>> > frequency suspend/resume dance or is that happening just when you let the
>> > machine run forever as well?
>>
>> We couldn't devise any reproduction steps. We observed it happening at
>> unexpected times in a fleet of devices -- and we couldn't find any
>> patterns to clue us in.
>
> Ok. Did you talk to NXP about that? Or did you try to exercise reads in a
> loop to detect the wreckage and maybe a pattern in there?

Yes, we talked to NXP about it. They don't have a conclusion on what happened.
While they've been very helpful... we were off the path from their reference
implementation and so it's not a high priority for them.

No, we didn't try that because we prioritized the "persistent clock" approach.
I have a little more time now and can try the loop-reading strategy.

-gabe