Il 25/11/2013 16:07, 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.
Yes, that makes sense because it avoids unnecessary COW. > 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. I think it is fine to increase it to the cluster_size or even to the optimal transfer length (new BlockLimits field). > 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. I think composing the optimal transfer length and optimal unmap granularity (cluster_size) will work well: * clamp maximum size to optimal transfer length * then, round final sector down to unmap granularity Paolo
