Messages in this thread | | | Date | Mon, 02 Jan 2012 17:18:13 +0100 | From | Paolo Bonzini <> | Subject | Re: [PATCH 0/6][RFC] virtio-blk: Change I/O path from request to BIO |
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On 01/02/2012 05:15 PM, Christoph Hellwig wrote: > > When QEMU uses O_DIRECT, the guest should not use QUEUE_FLAG_NONROT > > unless it is active for the host disk as well. (In doubt, as is the > > case for remote hosts accessed over NFS, I would also avoid NONROT > > and allow more coalescing). > > Do we have any benchmark numbers where QUEUE_FLAG_NONROT makes a > difference?
Not that I know of.
> I tried a few times, and the only constant measureable > thing was that it regressed performance when used for rotating devices > in a few benchmarks.
Were you trying with cache=none or writeback? For cache=none, that's exactly what I'd expect. cache=writeback could be more interesting...
Paolo
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