Re: [ANNOUNCE] kvm-14 release

Anthony Liguori
2007-02-21T15:31:21Z

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
>
> ------------------------------------------------------------------------
>
> -------------------------------------------------------------------------
> Take Surveys. Earn Cash. Influence the Future of IT
> Join SourceForge.net's Techsay panel and you'll get the chance to share your
> opinions on IT & business topics through brief surveys-and earn cash
> http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
> ------------------------------------------------------------------------
>
> _______________________________________________
> kvm-devel mailing list
> kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
> https://lists.sourceforge.net/lists/listinfo/kvm-devel