[Qemu-devel] Re: [kvm-devel] [PATCH 0/4] Rework alarm timer infrastrucure - take2

[Luca <kronos.it@gmail.com>]

On 8/22/07, Avi Kivity <avi@qumranet.com> wrote:
> Luca Tettamanti wrote:
> > Il Wed, Aug 22, 2007 at 08:02:07AM +0300, Avi Kivity ha scritto:
> >
> >> Luca Tettamanti wrote:
> >>
> >>
> >>> Actually I'm having troubles with cyclesoak (probably it's calibration),
> >>> numbers are not very stable across multiple runs...
> >>>
> >>>
> >> I've had good results with cyclesoak; maybe you need to run it in
> >> runlevel 3 so the load generated by moving the mouse or breathing
> >> doesn't affect meaurements.
> >>
> >
> > This is what I did, I tested with -no-grapich in text console.
>
> Okay.  Maybe cpu frequency scaling confused it then. Or something else?

I set it performance, frequency was locked at 2.1GHz.

> >>> The guest is an idle kernel with HZ=1000.
> >>>
> >>>
> >> Can you double check this?  The dyntick results show that this is either
> >> a 100Hz kernel, or that there is a serious bug in dynticks.
> >>
> >
> > Ops I sent the wrong files, sorry.
> >
> > This is QEMU, with dynticks and HPET:
> >
> > % time     seconds  usecs/call     calls    errors syscall
> > ------ ----------- ----------- --------- --------- ----------------
> >  52.10    0.002966           0     96840           clock_gettime
> >  19.50    0.001110           0     37050           timer_gettime
> >  10.66    0.000607           0     20086           timer_settime
> >  10.40    0.000592           0      8985      2539 sigreturn
> >   4.94    0.000281           0      8361      2485 select
> >   2.41    0.000137           0      8362           gettimeofday
> > ------ ----------- ----------- --------- --------- ----------------
> > 100.00    0.005693                179684      5024 total
> >
>
> This looks like 250 Hz?

Nope:

# CONFIG_NO_HZ is not set
# CONFIG_HZ_100 is not set
# CONFIG_HZ_250 is not set
# CONFIG_HZ_300 is not set
CONFIG_HZ_1000=y
CONFIG_HZ=1000

and I'm reading it from /proc/config.gz on the guest.

> And a huge number of settime calls?

Yes, maybe some QEMU timer is using an interval < 1ms?
Dan do you any any idea of what's going on?

Luca