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

[Dou Liyang]

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