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

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Message-ID: <CAJWu+or1BvDFLVJkQa5awXV4=-pHi5-LFcEmVxu8pDKqhoOx9Q@mail.gmail.com>
Date:   Fri, 6 Jan 2017 18:39:57 -0800
From:   Joel Fernandes <joelaf@...gle.com>
To:     John Stultz <john.stultz@...aro.org>
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

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.

Regards,
Joel