Re: [PATCH v2] scripts/simplebench: compare write request performance

[Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>]

On 13.07.2020 11:43, Vladimir Sementsov-Ogievskiy wrote:
> 12.07.2020 19:07, Andrey Shinkevich wrote:
>> On 11.07.2020 16:05, Vladimir Sementsov-Ogievskiy wrote:
>>> 26.06.2020 17:31, Andrey Shinkevich wrote:
>>>> The script 'bench_write_req.py' allows comparing performances of write
>>>> request for two qemu-img binary files.
>>>> An example with (qemu-img binary 1) and without (qemu-img binary 2) 
>>>> the
>>>> applied patch "qcow2: skip writing zero buffers to empty COW areas"
>>>> (git commit ID: c8bb23cbdbe32f5)
>>>> The <unaligned> case does not involve the COW optimization.
>>>>
>>> Good, this proves that c8bb23cbdbe32f5 makes sense.
>>>
>>>> Suggested-by: Denis V. Lunev <den@openvz.org>
>>>> Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>>> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
>>>> ---
>>>> v2:
>>>>    01: Three more test cases added to the script:
>>>>        <simple case>
>>>>        <general case>
>>>>        <unaligned>
>>>>
>>>>   scripts/simplebench/bench_write_req.py | 201 
>>>> +++++++++++++++++++++++++++++++++
>>>>   1 file changed, 201 insertions(+)
>>>>   create mode 100755 scripts/simplebench/bench_write_req.py
>>>>
>>>> diff --git a/scripts/simplebench/bench_write_req.py 
>>>> b/scripts/simplebench/bench_write_req.py
>>>> new file mode 100755
>>>> index 0000000..fe92d01
>>>> --- /dev/null
>>>> +++ b/scripts/simplebench/bench_write_req.py
>>>> @@ -0,0 +1,201 @@
>>>
>>> Next, I don't understand, are you trying to fill qcow2 image by dd 
>>> directly? This is strange. Even if you don't break metadata, you 
>>> don't change it, so all cluster will remain empty.
>>>
>>>
>> I have tested and it works as designed.
>>
>
> But how is it designed? You just filled unallocated clusters with some 
> data. When you read from qcow2, you'll still read zeros, because L1/L2 
> tables are not filled. The random data will lay untouched.
>
>
>> This dd command doesn't hurt the metadata and fills the image with 
>> random data. The actual disk size becomes about 1G after the dd command.
>>
If patch 0001 is OK in v4, I can remove the patches 0002 and 0003 with 
the 'unaligned' test case as an unnecessary one.

Andrey