On 16/12/2014 14:10, Kevin Wolf wrote:
> Am 16.12.2014 um 12:28 hat Paolo Bonzini geschrieben:
>>
>>
>> On 16/12/2014 12:07, Kevin Wolf wrote:
>>> Am 11.12.2014 um 14:52 hat Paolo Bonzini geschrieben:
>>>> Keep a queue of requests that were not submitted; pass them to
>>>> the kernel when a completion is reported, unless the queue is
>>>> plugged.
>>>>
>>>> The array of iocbs is rebuilt every time from scratch. This
>>>> avoids keeping the iocbs array and list synchronized.
>>>>
>>>> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
>>>
>>> Just found out that in qemu-img bench, this patch seems to cost about
>>> 5-8% for me.
>>
>> What execution? Queue depth=1?
>
> My usual one:
>
> $ ./qemu-img bench -t none -c 10000000 -n /dev/loop0
> Sending 10000000 requests, 4096 bytes each, 64 in parallel
I could reproduce this very well on a random OS image that I had around.
This is raw over XFS over dm-crypt, and the image is about 75% sparse
(8.2G used over 35G). I only get 1-2%, but still it's visible.
However I can hardly reproduce it when using a partition directly:
old new
mean 9.9565 9.9636 (+0.07%)
stddev 0.0405 0.0537
min 9.871 9.867
median 9.973 9.971
max 10.01 10.053
count 20 20
I haven't tried removing layers (e.g. fully-allocated XFS image without
dm-crypt).
Paolo
