Re: [kvm-devel] [patch 2/2] QEMU: decrease console "refresh rate" with -nographic

[Avi K. <av...@qu...>]

Anders wrote:
> Avi Kivity wrote:
>
>   
>> if select() doesn't enable signals (like you can do with pselect) you
>> may sit for a long time in select() until the timer expires.
>>     
>
> Hm. Does the guest timer affect host userspace in all configurations? The
> original trigger for my SIGIO patch was that opening a VNC connection
> would take up to a second, until the qemu RTC timer fired.
>
>   

Right, if the guest is using the lapic or pit timers, there is no 
periodic signal to userspace.

>   
>> Consider a 100Hz Linux guest running 'ls -lR' out of a cold cache:
>> instead of 1-2 ms disk latencies you'll see 10 ms latencies, killing
>> performance by a factor of 5.
>>     
>
> I guess this works out even worse for a dyntick guest?
>
>
>   

Yes.  We can't depend on guest activity for correctness.


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