Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size

[Peter Lieven]

On 25.11.2013 15:54, Paolo Bonzini wrote:
> Il 25/11/2013 14:57, Peter Lieven ha scritto:
> > since the convert process is basically a sync operation it might
> > be benificial in some case to change the hardcoded I/O buffer
> > size to an alternate (greater) value.
> Do you really need the extra knob?  You can just add to BlockLimits the
> optimal transfer length, and use it unconditionally.
If you say patch 5 and 3 are ok. What could be done is to remove
this knob and increase the iobuf_size to cluster_size if cluster_size
is greater. I do not want to increase the default iobuf size to anything
greater than 2MB. I do not know why this was choosen, but maybe
there was a reason for it.

The storages we use here have a very strange page size of 15MB.
If I sent aligned 15MB chunks the performace is about +50% compared
to the original qemu-img.

Peter