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

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Date:   Thu, 5 Oct 2017 23:33:55 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Gabriel Beddingfield <gabe@...tlabs.com>
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, 5 Oct 2017, Thomas Gleixner wrote:
> On Thu, 5 Oct 2017, Gabriel Beddingfield wrote:
> 
> > Hi Thomas,
> > 
> > On Thu, Oct 5, 2017 at 11:01 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > >> > Which SoC/clocksource driver are you talking about?
> > >>
> > >> NXP i.MX 6SoloX
> > >> drivers/clocksource/timer-imx-gpt.c
> > >
> > > 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?

The reason I'm asking is to exclude any weird issue in the timekeeping
code, which is still a possibility, despite the fact that I went through it
with a fine comb after stumbling over that check in the resume path.

Thanks,

	tglx