linux-kernel - Re: [PATCH v3 1/3] timekeeping: Add a fast and NMI safe boot clock

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Message-ID: <CALAqxLW+25HQdbuWqqRo0WwR+8c1X4EX8z_=sCNN8MKnE00mWQ@mail.gmail.com>
Date:   Fri, 6 Jan 2017 16:48:56 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "Christopher S. Hall" <christopher.s.hall@...el.com>,
        Baolin Wang <baolin.wang@...aro.org>
Subject: Re: [PATCH v3 1/3] timekeeping: Add a fast and NMI safe boot clock

On Thu, Nov 24, 2016 at 12:20 PM, Joel Fernandes <joelaf@...gle.com> wrote:
> This boot clock can be used as a tracing clock and will account for
> suspend time.
>
> To keep it NMI safe since we're accessing from tracing, we're not using a
> separate timekeeper with updates to monotonic clock and boot offset
> protected with seqlocks. This has the following minor side effects:
>
> (1) Its possible that a timestamp be taken after the boot offset is updated
> but before the timekeeper is updated. If this happens, the new boot offset
> is added to the old timekeeping making the clock appear to update slightly
> earlier:
>    CPU 0                                        CPU 1
>    timekeeping_inject_sleeptime64()
>    __timekeeping_inject_sleeptime(tk, delta);
>                                                 timestamp();
>    timekeeping_update(tk, TK_CLEAR_NTP...);
>
> (2) On 32-bit systems, the 64-bit boot offset (tk->offs_boot) may be
> partially updated.  Since the tk->offs_boot update is a rare event, this
> should be a rare occurrence which postprocessing should be able to handle.
>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: John Stultz <john.stultz@...aro.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Signed-off-by: Joel Fernandes <joelaf@...gle.com>

Hey Joel,
  Hope you had a good new years! I was queuing this up for testing,
and the patch set no longer applies (to v4.10-rc2). Can you respin it
and resend it?

thanks
-john