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

[Dou Liyang <douly.fnst@cn.fujitsu.com>]

Hi Pasha,

Sorry to reply you so late.

I have test the TSC sync in our machine with DR(Dynamic Reconfiguration)
   Linux kernel: Linux-4.14.0-rc5
   NUMA nodes: 4 node.
   Use clock_gettime() to reach nano-second accuracy.

It is OK that we setup our reconfigurable with "tsc=unstable".

Thanks,
	dou.

At 09/29/2017 11:00 PM, Dou Liyang wrote:
> Hi, Pasha
>
> At 09/28/2017 09:11 PM, Pasha Tatashin wrote:
>>>>> It will be best if we can support TSC sync capability in x86, but
>>>>> seems
>>>>> is not easy.
>>>>
>>>> Sure, your hardware achieving sync would be best, but even if it does
>>>> not, we can still use TSC. Using notsc simple because you fail to sync
>>>> TSCs is quite crazy.
>>>>
>>>> The thing is, we need to support unsync'ed TSC in any case, because
>>>> older chips (pre Nehalem) didn't have synchronized TSC in any case, and
>>>> it still happens on recent chips if the BIOS mucks it up, which happens
>>>> surprisingly often :-(
>>>>
>>>> I would suggest you try your reconfigurable setup with "tsc=unstable"
>>>> and see if that works for you. That marks the TSC unconditionally
>>>> unstable at boot and avoids any further wobbles once the TSC watchdog
>>>> notices (although that too _should_ more or less work).
>>>
>>> That should do the trick nicely and we might just end up converting
>>> notsc
>>> to tsc=unstable silently so we can avoid the bike shed discussions about
>>> removing it.
>>>
>>
>> Ok, I will start working on converting notsc to unstable, and modify my
>> patches to do what Peter suggested earlier. In the mean time, I'd like
>> to hear from Dou if this setup works with dynamic reconfig.
>>
>
> OK, I will do it, But, October 1 is our national holiday, I will in
> holiday, and I just returned the test machine. :-(
>
> May reply you in middle of the October.


>
> Thanks,
>
>     dou.
>
>> Thank you,
>> Pasha
>>
>>
>>