Messages in this thread | | | Subject | Re: [PATCH v6 1/4] sched/clock: interface to allow timestamps early in boot | From | Pasha Tatashin <> | Date | Wed, 27 Sep 2017 13:13:15 -0400 |
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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 >
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