On Mon, Jan 02, 2012 at 05:12:00PM +0100, Paolo Bonzini wrote: > On 01/01/2012 05:45 PM, Stefan Hajnoczi wrote: > >By the way, drivers for solid-state devices can set QUEUE_FLAG_NONROT > >to hint that seek time optimizations may be sub-optimal. NBD and > >other virtual/pseudo device drivers set this flag. Should virtio-blk > >set it and how does it affect performance? > > By itself is not a good idea in general. > > 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? 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. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
