Re: [Qemu-devel] [RFC PATCH v2 00/23] qcow2: Delayed COW

[Stefan Hajnoczi]

On Thu, Feb 14, 2013 at 11:56:34AM +0100, Kevin Wolf wrote:
> Am 14.02.2013 11:43, schrieb Stefan Hajnoczi:
> > On Wed, Feb 13, 2013 at 02:21:50PM +0100, Kevin Wolf wrote:
> >> iozone results with and without this series show significant difference
> >> for allocating writes:
> >>
> >>                                                          random  random
> >>            KB  reclen   write rewrite    read    reread    read   write
> >>
> >> base    65536       8    1727    1945    12546    12539    2449    1836
> >> patch   65536       8    1934    1949    12263    12521    2463    1796
> >>
> >> base  1048576     256   22344   38437   105823   106135   37743   32167
> >> patch 1048576     256   35989   38542   105231   105994   38301   33036
> > 
> > I imagine the benefit is even greater for 4 KB or 8 KB blocksize?
> 
> The upper two lines are 8k block size. I suspect that the benefit would
> be the greatest for misaligned 64k writes, then you have one overlapping
> allocation for each issued request.

I see.  I haven't looked at IOzone output for too long, forgot how to
interpret it.

Stefan