RE: [Xen-devel] Re: [Xen-users] About profiling xen

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> Is there a way to make available a better timer (hpet,acpi....)?
> 
> Also, on another xen box (rhel 5.2), I've a 'pit' clocksource in
> available_clocksource.
> After:
> # sysctl -w xen.independent_wallclock=1
> 
> and
> --------------------------------------------------------------
> ----------------------------------------------------------------------
> # echo pit > 
> /sys/devices/system/clocksource/clocksource0/current_clocksource
> [root@station1 init.d]# cat
> /sys/devices/system/clocksource/clocksource0/current_clocksource
> jiffies
> --------------------------------------------------------------
> ----------------------------------------------------------------------
> 
> the clocksource is unmodified.
> 

Because of save/restore and migrate, no hardware timer is
suitable for a pv domain.  The code that is handling the
clock is the paravirtualized clock code (aka pvclock).
Nobody ever changed the sysfs reporting mechanism in
pv versions of released Red Hat kernels, so clocksource
gets reported as "jiffies", and even though "pit"
appears to be available, it is not (since it wouldn't
work).  I suspect this is also the case for other
distros' pv kernels.

Dan

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