Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early in boot

From	Pasha Tatashin <pasha.tatashin@oracle.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early in boot
Date	2017-09-27 19:20 +0200
Message-ID	<uuoa5-60L-3@gated-at.bofh.it> (permalink)
References	(1 earlier) <ukfB8-3fk-31@gated-at.bofh.it> <uuk6u-2Hs-1@gated-at.bofh.it> <uukpP-3b4-5@gated-at.bofh.it> <uukpP-3b4-3@gated-at.bofh.it> <uul2x-3HA-9@gated-at.bofh.it>
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Hi Dou,

This makes sense. The current sched_clock_early() approach does not 
break it because with notsc TSC is used early in boot, and later 
stopped. But, notsc must stay.

Peter,

So, we could either expend sched_clock() with another static branch for 
early clock, or use what I proposed. IMO, the later is better, but 
either way works for me.

Thank you,
Pasha

On 09/27/2017 09:52 AM, Dou Liyang wrote:
> Hi Pasha, Peter
> 
> At 09/27/2017 09:16 PM, Pasha Tatashin wrote:
>> Hi Peter,
>>
>> I am totally happy with removing notsc. This certainly simplifies the
>> sched_clock code. Are there any issues with removing existing kernel
>> parameters that I should be aware of?
>>
> 
> We do not want to do that. Because, we use "notsc" to support Dynamic
> Reconfiguration[1].
> 
> AFAIK, this feature enables hot-add system board which contains CPUs
> and memories. But the CPUs in different board may have different TSCs
> which are not consistent with the TSC from the existing CPUs. If we 
> hot-add a board directly, the machine may happen the inconsistency of
> TSC.
> 
> We make our effort to specify the same TSC value as existing one through
> hardware and firmware, but it is hard. So we recommend to specify
> "notsc" option in command line for users who want to use Dynamic
> Reconfiguration.
> 
> [1] 
> http://www.fujitsu.com/global/products/computing/servers/mission-critical/primequest/technology/availability/dynamic-reconfiguration.html 
>

Thread

Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Peter Zijlstra <peterz@infradead.org> - 2017-09-27 15:00 +0200
  Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Pasha Tatashin <pasha.tatashin@oracle.com> - 2017-09-27 15:20 +0200
    Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Dou Liyang <douly.fnst@cn.fujitsu.com> - 2017-09-27 16:00 +0200
      Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Pasha Tatashin <pasha.tatashin@oracle.com> - 2017-09-27 19:20 +0200
      Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Peter Zijlstra <peterz@infradead.org> - 2017-09-27 20:10 +0200
        Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Peter Zijlstra <peterz@infradead.org> - 2017-09-27 20:20 +0200
          Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Dou Liyang <douly.fnst@cn.fujitsu.com> - 2017-09-28 12:10 +0200
            Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Peter Zijlstra <peterz@infradead.org> - 2017-09-28 14:00 +0200
              Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Thomas Gleixner <tglx@linutronix.de> - 2017-09-28 14:20 +0200
                Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Pasha Tatashin <pasha.tatashin@oracle.com> - 2017-09-28 15:20 +0200
                Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Dou Liyang <douly.fnst@cn.fujitsu.com> - 2017-09-29 17:10 +0200
  Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early  in boot Peter Zijlstra <peterz@infradead.org> - 2017-09-27 15:20 +0200

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