Re: AIO for better disk IO? Re: [Xen-users] Getting better Disk IO

[Goswin von Brederlow <brederlo@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

"Petersson, Mats" <Mats.Petersson@xxxxxxx> writes:

>> -----Original Message-----
>> From: Liang Yang [mailto:multisyncfe991@xxxxxxxxxxx] 
>>...
>> Second Question:
>> Does Domain0 always wait till AIO data is available and then 
>> notify guest
>> domain? or Domain0 will issue an interrupt immediately to notify guest
>> domain0 when AIO is queued? If the first case is true, then 
>> all AIOs will
>> become synchronous.
>
> The guest can not be issued with an interrupt to signify "data
> available" until the guest's data has been read, so for reads at least,
> the effect from the guest's perspective is still synchronous. This
> doesn't mean that the guest can't issue further requests (for example
> from a different thread, or simply queuing multiple requests to the
> device) and gain from the fact that these requests can be started before
> the first issued request is completed (from the backend drivers point of
> view). 

So, to name something familiar, you gain a (very long) command queue. 

MfG
        Goswin

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