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...
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