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

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 09/30/09 02:06, Marco Tizzoni wrote:
> Enabling debug on kernel I realized the problem is related to timer accuracy.
> ------------------------------------------------------------------------
> hal9k-dom0 ~ # cat /proc/timer_list
> Timer List Version: v0.3
> HRTIMER_MAX_CLOCK_BASES: 2
> now at 784689453083 nsecs
>
> cpu: 0
>  clock 0:
>  .index:      0
>  .resolution: 999848 nsecs
> [........]
> hal9k-dom0 ~ # cat
> /sys/devices/system/clocksource/clocksource0/available_clocksource
> xen jiffies
> hal9k-dom0 ~ # cat
> /sys/devices/system/clocksource/clocksource0/current_clocksource
> xen
> ------------------------------------------------------------------------
>
> Is there a way to make available a better timer (hpet,acpi....)?
>   

Your clocksource is "xen", which is the best possible for a PV xen guest.

However, a clocksource is for measuring elapsed time, not triggering
timers.  Unfortunately there doesn't seem to be a /sys file to show the
current clockevent source in use, but if you have "xen" clocksource it's
almost certainly the xen clockevent.

However, this is only relevent if you have CONFIG_NO_HZ and
CONFIG_HIGHRES_TIMERS enabled.  If you don't then all timers will be
quantized to HZ (and your guests will burn lots CPU being needlessly
interrupted at HZ).

    J