Anthony Liguori wrote:
> Laurent Vivier wrote:
>> Avi Kivity wrote:
>>   
>>> Aurelien Jarno wrote:
>>>     
>>>>   
>>>>       
>>>>> What is your disk image file format, or are you using a partition?
>>>>>     
>>>>>         
>>>> I am using a raw image file on an ext3 partition.
>>>>
>>>>   
>>>>       
>>>>> Do the results change (on kvm-14) if you pin the guest to a core with 
>>>>> 'taskset 1 qemu ...'
>>>>>     
>>>>>         
>>>> Bingo. It now works even faster than kvm-13!
>>>>
>>>> real    0m22.307s
>>>> user    0m13.935s
>>>> sys     0m4.720
>>>>
>>>>   
>>>>       
>>> I'm guessing this is due to the glibc aio implementation, which uses 
>>> threads instead of true aio.  The threads may cause the vcpu to migrate 
>>> frequently from one code to another.
>>>
>>> There are two possible solutions:
>>>
>>>  - use native aio from http://www.bullopensource.org/posix/.  I think 
>>> the aio signal patches are not yet in, so this may not work.
>>>  - teach the scheduler about the cost of migrating vcpus
>>> The first approach will solve itself eventually, though slowly if the 
>>> current slow rate of aio merging continues.  We'll have to do the second.
>>>
>>>     
>> if you prefer the first one, Sébastien will release very soon aio patches for
>> 2.6.20 with an up-to-date libposix-aio.
>>   
> 
> Hi Laurent,

Hi Anthony,

> I gave that a shot a little bit ago.  Ran into two problems.
> 
> 1) Couldn't avoid linking to -lrt as QEMU uses time functions from it.
> 2) While I could get things compiling (with patches), QEMU would SEGV 
> almost immediately.
> 
> Could you guys maybe give compiling QEMU w/libposix-aio a shot?  I'm 
> really interested to see if it makes a difference.

Ok, I take a look at this.

Regards,
Laurent
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