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

[Kevin Wolf]

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.

Kevin