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

From	Dou Liyang <douly.fnst@cn.fujitsu.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early in boot
Date	2017-09-28 12:10 +0200
Message-ID	<uuDVv-7Gp-1@gated-at.bofh.it> (permalink)
References	(3 earlier) <uukpP-3b4-5@gated-at.bofh.it> <uukpP-3b4-3@gated-at.bofh.it> <uul2x-3HA-9@gated-at.bofh.it> <uuoWu-6xJ-7@gated-at.bofh.it> <uup6a-6B0-21@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Hi Peter,

At 09/28/2017 02:09 AM, Peter Zijlstra wrote:
> On Wed, Sep 27, 2017 at 08:05:48PM +0200, Peter Zijlstra wrote:
>> On Wed, Sep 27, 2017 at 09:52:36PM +0800, Dou Liyang wrote:
>>> 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.
>>
>> Oh gawd, that's horrific. And in my book a good reason to kill that
>> option.
>
> That is, even with unsynchronized TSC we're better off using RDTSC. The
> whole mess in kernel/sched/clock.c is all about getting semi sensible
> results out of unsynchronized TSC.
>

It will be best if we can support TSC sync capability in x86, but seems
is not easy.

Thanks,

	dou.

> There really is no reason to artificially kill TSC usage.
>
>
>

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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