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

From: Dou Liyang
Date: Wed Oct 18 2017 - 06:01:29 EST


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