Messages in this thread | | | Date | Fri, 13 Apr 2012 11:33:28 -0700 | Subject | Re: [PATCH] xen: always set the sched clock as unstable | From | Sheng Yang <> |
| |
On Fri, Apr 13, 2012 at 11:20 AM, David Vrabel <david.vrabel@citrix.com> wrote: > > From: David Vrabel <david.vrabel@citrix.com> > > The sched clock was considered stable based on the capabilities of the > underlying hardware. This does not make sense for Xen PV guests as: > a) the hardware TSC is not used directly as the clock source; and b) > guests may migrate to hosts with different hardware capabilities. > > It is not clear to me whether the Xen clock source is supposed to be > stable and whether it should be stable across migration. For a clock > source to be stable it must be: a) monotonic; c) synchronized across > CPUs; and c) constant rate. > > There have also been reports of systems with apparently unstable > clocks where clearing sched_clock_stable has fixed problems with > migrated VMs hanging. > > So, always set the sched clock as unstable when using the Xen clock > source. > > Signed-off-by: David Vrabel <david.vrabel@citrix.com> > --- > arch/x86/xen/time.c | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c > index 0296a95..8469b5a 100644 > --- a/arch/x86/xen/time.c > +++ b/arch/x86/xen/time.c > @@ -473,6 +473,7 @@ static void __init xen_time_init(void) > do_settimeofday(&tp); > > setup_force_cpu_cap(X86_FEATURE_TSC); > + sched_clock_stable = 0; > > xen_setup_runstate_info(cpu); > xen_setup_timer(cpu); > -- > 1.7.2.5 >
(Sorry for duplicate posts, gmail is really not a ideal client for lkml - though exchange is worse...)
I really prefer to hide nonstop tsc feature from Xen side, rather than let Linux kernel to have a condition that "Nonstop TSC feature existed, but sched_clock_stable=0".
For the other context, please refer to the discussion at xen-devel.
http://lists.xen.org/archives/html/xen-devel/2012-04/msg00888.html http://lists.xen.org/archives/html/xen-devel/2012-04/msg00969.html
-- regards Yang, Sheng -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |