[libvirt] PATCH: Disable QEMU drive caching
Anthony Liguori
anthony at codemonkey.ws
Thu Oct 9 14:06:42 UTC 2008
Anthony Liguori wrote:
> Mark McLoughlin wrote:
>
> And let's take a step back too. If people are really concerned about
> this point, let's introduce a sync=on option that opens the image with
> O_SYNC. This will effectively make the cache write-through without
> the baggage associated with O_DIRECT.
I'm starting to slowly convince myself we should always open files with
O_SYNC. Barriers should just force ordering within the thread pool.
posix-aio has no interface for this but we could create one with our own
thread pool implementation.
Ryan: could you give the following patch a perf-run so we can see how
this would effect us?
Thanks,
Anthony Liguori
> While I object to libvirt always setting cache=off, I think sync=on
> for IDE and SCSI may be reasonable (you don't want it for virtio-blk
> once we implement proper barriers with fdatasync I think).
>
> Regards,
>
> Anthony Liguori
>
>> Cheers,
>> Mark.
>>
>>
>
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