Messages in this thread | | | Date | Mon, 16 Apr 2012 10:30:35 -0700 (PDT) | From | Dan Magenheimer <> | Subject | RE: [Xen-devel] [PATCH] xen: always set the sched clock as unstable |
| |
> From: David Vrabel [mailto:david.vrabel@citrix.com] > Subject: Re: [Xen-devel] [PATCH] xen: always set the sched clock as unstable > > On 16/04/12 17:05, Dan Magenheimer wrote: > >> From: David Vrabel [mailto:david.vrabel@citrix.com] > >> Subject: Re: [Xen-devel] [PATCH] xen: always set the sched clock as unstable > > > > Nacked-by: Dan Magenheimer <dan.magenheimer@oracle.com> > > Fair enough, > > > [A stable clock] should be true for Xen 4.0+ (but not for pre-Xen-4.0). > > The original customer problem is on a host with Xen 3.4. What do you > recommend for Linux guests running such hosts?
For pre-Xen-4.0 and an unchanged PV guest, I don't know. If you can back-patch the guest kernel with a workaround such as your patch, great! I'm only arguing against the patch getting perpetuated upstream.
> > In fact, it might be wise for a Xen-savvy kernel to check to see > > if it is running on Xen-4.0+ and, if so, force clocksource=tsc > > and tsc=reliable. > > So, should the xen clocksource do: > > if Xen 4.0+ > clock is stable, use rdtsc only. > else > clock is unstable, use existing pvclock implementation.
Yes, that's what I propose. To clarify:
if the guest can and does determine it is running on Xen 4.0+ TSC is guaranteed by Xen to be stable, use clocksource=tsc tsc=reliable else Xen only guarantees that pvclock is stable, use pvclock
| |