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

Avi Kivity
2007-08-19T08:24:18Z

Anthony Liguori wrote:
> I think this is a really nice and important patch set. Just a couple
> things:
>
> On Sun, 2007-08-19 at 00:02 +0200, Luca Tettamanti wrote:
>
>
>>> In this case the dyn-tick minimum res will be 1msec. I believe it should
>>> work ok since this is the case without any dyn-tick.
>>>
>> Actually minimum resolution depends on host HZ setting, but - yes -
>> essentially you have the same behaviour of the "unix" timer, plus the
>> overhead of reprogramming the timer.
>>
>
> Is this significant? At a high guest HZ, this is could be quite a lot
> of additional syscalls right?
>
>

At HZ=1000, this adds a small multiple of 1000 syscalls, which is a
fairly small overhead. At HZ>1000 (only possible with a dyntick guest),
the current implementation doesn't cope at all, so we can't compare
overhead.

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