Re: [Qemu-devel] [PATCH] qcow2: improve I/O performance with cache=off

[Kevin Wolf]

Hi Laurent,

Laurent Vivier schrieb:
> this patch improves qcow2 I/O performance when used with cache=off.

Why do you think this patch helps only for cache=off? I have applied
your patch to Xen ioemu (which has no cache=off / O_DIRECT yet) and
I certainly do see a performance gain for large block sizes (using dd).
With small block sizes like 512 bytes or 1k I lose a bit of perfomance,
though.

bonnie++ shows slightly better numbers with this patch, too. In the
case of block reads the improvement is huge and I even got double
throughput.

I also had a look at your code and it seems fine to me. (Except that
the aio callback handlers become even longer, but that is a different
problem...)

Kevin