Re: [Qemu-devel] [Qemu-block] [PATCH v5 0/2] block: enforce minimal 4096 alignment in qemu_blockalign

[Paolo Bonzini]

On 13/05/2015 17:43, Stefan Hajnoczi wrote:
> A 64 MB buffer was given in the pwrite() call.
> 
> The first and the last 128-page write requests may have partial
> pages, but why should the rest not use fully aligned 1024 sector
> writes?
> 
> Maybe the buffer is split by the max sectors per request before
> the alignment requirements are considered.  It would be more
> efficient to first split off the unaligned parts.

Sounds like this could be it---then it's very similar to the issue
fixed by kernel commit c6e666345e1b (block: split discard into aligned
requests, 2012-08-02).

Paolo