linux-kernel - Re: [RFC/RFT patch 0/7] timekeeping: Unify clock MONOTONIC and clock BOOTTIME

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Date:   Fri, 20 Apr 2018 06:37:12 +0200
From:   David Herrmann <dh.herrmann@...il.com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Kevin Easton <kevin@...rana.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Jonathan Corbet <corbet@....net>
Subject: Re: [RFC/RFT patch 0/7] timekeeping: Unify clock MONOTONIC and clock BOOTTIME

Hey

On Tue, Mar 13, 2018 at 7:11 PM, John Stultz <john.stultz@...aro.org> wrote:
> On Mon, Mar 12, 2018 at 11:36 PM, Ingo Molnar <mingo@...nel.org> wrote:
>> Ok, I have edited all the changelogs accordingly (and also flipped around the
>> 'clock MONOTONIC' language to the more readable 'the MONOTONIC clock' variant),
>> the resulting titles are (in order):
>>
>>  72199320d49d: timekeeping: Add the new CLOCK_MONOTONIC_ACTIVE clock
>>  d6ed449afdb3: timekeeping: Make the MONOTONIC clock behave like the BOOTTIME clock
>>  f2d6fdbfd238: Input: Evdev - unify MONOTONIC and BOOTTIME clock behavior
>>  d6c7270e913d: timekeeping: Remove boot time specific code
>>  7250a4047aa6: posix-timers: Unify MONOTONIC and BOOTTIME clock behavior
>>  127bfa5f4342: hrtimer: Unify MONOTONIC and BOOTTIME clock behavior
>>  92af4dcb4e1c: tracing: Unify the "boot" and "mono" tracing clocks
>>
>> I'll push these out after testing.
>
> I'm still anxious about userspace effects given how much I've seen the
> current behavior documented, and wouldn't pushed for this myself (I'm
> a worrier), but at least I'm not seeing any failures in initial
> testing w/ kselftest so far.

I get lots of timer-errors on Arch-Linux booting current master, after
a suspend/resume cycle. Just a selection of errors I see on resume:

systemd[1]: systemd-journald.service: Main process exited,
code=dumped, status=6/ABRT
rtkit-daemon[742]: The canary thread is apparently starving. Taking action.
systemd[1]: systemd-udevd.service: Watchdog timeout (limit 3min)!
systemd[1]: systemd-journald.service: Watchdog timeout (limit 3min)!
kernel: e1000e 0000:00:1f.6: Failed to restore TIMINCA clock rate delta: -22

Lots of crashes with SIGABRT due to these.

I did not bisect it, but it sounds related to me. Also, user-space
uses CLOCK_MONOTONIC for watchdog timers. That is, a process is
required to respond to a watchdog-request in a given MONOTONIC
time-frame. If this jumps during suspend/resume, watchdogs will fire
immediately. I don't see how this can work with the new MONOTONIC
behavior?

Thanks
David