Re: [ANNOUNCE] kvm-14 release

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

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,

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.

Regards,

Anthony Liguori

> [advertising] Keep an eye on the bullopensource website. [/advertising]
> :-P
>
> Regards,
> Laurent
>   
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