On Fri, Jan 20, 2017 at 05:39:40PM +0100, Paolo Bonzini wrote:
> 
> 
> On 19/01/2017 18:01, Stefan Hajnoczi wrote:
> >>> This is a big and somewhat risky change.  Have you run any performance
> >>> benchmarks?
> >>
> >> Not recently; I ran them a year ago and there was no measurable difference.
> > 
> > Good, please re-run for the final version.
> 
> Done, went better than expected. :)
> 
> base
> 4k-1 null   READ: io=6646.8MB, aggrb=226852KB/s, minb=226852KB/s, maxb=226852KB/s, mint=30000msec, maxt=30000msec
> 4k-1 nvme   READ: io=3086.4MB, aggrb=105342KB/s, minb=105342KB/s, maxb=105342KB/s, mint=30001msec, maxt=30001msec
> 4k-32 nvme  READ: io=14246MB, aggrb=486241KB/s, minb=486241KB/s, maxb=486241KB/s, mint=30001msec, maxt=30001msec
> 
> patched:
> 4k-1 null   READ: io=7044.5MB, aggrb=240436KB/s, minb=240436KB/s, maxb=240436KB/s, mint=30000msec, maxt=30000msec
> 4k-1 nvme   READ: io=3463.3MB, aggrb=118208KB/s, minb=118208KB/s, maxb=118208KB/s, mint=30001msec, maxt=30001msec
> 4k-32 nvme  READ: io=15217MB, aggrb=519378KB/s, minb=519378KB/s, maxb=519378KB/s, mint=30001msec, maxt=30001msec
> 
> null is null-co://, nvme is a fast (180kIOPS on bare-metal) NVMe SSD.
> 
> So it seems to be some 5-10% faster.  No idea why so I would not give too
> much importance on the numbers, but at least it's not worse.

Nice, thank you!

Stefan