Re: KVM power usage - high wakeup rates

[Avi Kivity <avi@qumranet.com>]

Anders wrote:
> Anthony Liguori wrote:
>> With the default options, my idle winxp guest causes about 550 
>> wakeups/sec which is pretty close to what I'd expect.  I don't think 
>> you'll get much better than that without using a dynticks guest.
>
> 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.

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

dyntick on both.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.