Re: Re: [PATCH] x86: unconditionally mark TSC unstable under Xen

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 07/15/2010 10:48 AM, Dan Magenheimer wrote:
> Maybe the xen_sched_clock code should be entirely removed
> rather than ifdef'd since it is no longer used and
> "(somewhat, in theory)" led to a strange bug?  Or if
> you are confident that it will be useful in the future
> by some linux scheduler, maybe add some comments about
> how enabling it may cause the effects Jed saw.

Yes, I can probably remove it altogether, though it isn't actually
selectable without manually editing the Kconfig file.

> And maybe an even better answer is to submit a patch upstream
> so that the scheduler doesn't use the same timebase for
> measuring both, since the kernel is making a bad assumption
> about real vs virtual time. I'd imagine KVM users might benefit
> from that also.

Its unclear how useful it is anyway.  I've discussed it with Peter
Zijlstra from time to time, but making the scheduler use two timebases
is non-trivial I think.  Or perhaps more accurate to say that I don't
want to be getting into the scheduler, since it is not only a
technical minefield.

    J