Re: KVM power usage - high wakeup rates

[Anders <mail@flac.kalibalik.dk>]

Avi Kivity wrote:
> Anders wrote:
>> According to powertop, I had about 15 kvm wakeups/sec with my 
>> previous setup (nohz, no display). Now I upgraded to kvm-70 and the 
>> timer interrupt has reappeared so I have this:
>>
>> Top causes for wakeups:
>>  25,4% (112,4)      <kernel IPI> : function call interrupts
>>  22,6% (100,0)   qemu-system-x86 : kvm_arch_vcpu_ioctl_run 
>> (pit_timer_fn)
>>  22,6% (100,0)   qemu-system-x86 : __kvm_migrate_timers (apic_timer_fn)
>>   8,7% ( 38,5)   qemu-system-x86 : sys_timer_settime (posix_timer_fn)
>>
>> What could be the cause for this change? The previous kvm was from 
>> Ubuntu 8.04, there are no changes in the guest.
>>
>
> Likely, the in-kernel pit.  Try -no-kvm-pit.

The -no-kvm-pit did change things. However, there is still a periodic tick:

Top causes for wakeups:
  34,7% (102,0)   qemu-system-x86 : sys_timer_settime (posix_timer_fn)
  34,0% (100,0)   qemu-system-x86 : __kvm_migrate_timers (apic_timer_fn)
  13,8% ( 40,7)      <kernel IPI> : function call interrupts

For comparison, this is my normal output. This is with the same kernel 
modules, but the userspace from Ubuntu 8.04:

Top causes for wakeups:
  50,2% ( 66,0)      <kernel IPI> : function call interrupts
  11,3% ( 14,9)               kvm : apic_mmio_write (apic_timer_fn)

>> In general, what are the best host/guest settings for a low number of 
>> wakeups?
>
> dyntick on both.
>

Sure. I guess my question was how to achieve that. Things like the 
-no-kvm-pit advice. Also, I have used "clocksource=tsc acpi=force" on 
the guest to get it to dyntick. But that seems to no longer work. So I 
was wondering whether there was some known configuration that was 
supposed to work.


Anders.