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

Avi Kivity
2008-04-16T11:23:39Z

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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