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

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Date:   Fri, 6 Jan 2017 20:02:20 -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 Fri, Jan 6, 2017 at 6:39 PM, Joel Fernandes <joelaf@...gle.com> wrote:
> Hi John,
>
> On Fri, Jan 6, 2017 at 4:48 PM, John Stultz <john.stultz@...aro.org> wrote:
>> 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,
>
> Thanks, yes I had a great new years, hope you did too.
>
>> and the patch set no longer applies (to v4.10-rc2). Can you respin it
>> and resend it?
>
> Actually these patches are already in 4.10-rc2.

Ha! Well, apologies for missing that over the holidays.

Sorry for the noise.
-john