Re: [Qemu-devel] [Bug 1321464] Re: qemu/block/qcow2.c:1942: possible performance problem ?

[Stefan Hajnoczi]

On Tue, May 20, 2014 at 11:21:05PM -0000, Max Reitz wrote:
> I can only speak for qcow2 and qcow, but for those places, I don't think
> it is worth fixing. First of all, both are image formats, so the
> bottleneck is generally the disk on which the images are stored and not
> main memory, so an overeager memset should not cause any problems.
> 
> For both, the relevant piece of code is in qcow2/qcow_write_compressed()
> which are rarely used anyway (as far as I know) and even if used, they
> have additional overhead due to having to compress data first, so
> “fixing” the memset() won't make them noticibly faster.

I agree.  It won't make a noticable difference and the compressed writes
are only done in qemu-img convert, not for running guests.

But patches to change this wouldn't hurt either.

Stefan