Re: [ANNOUNCE] kvm-14 release

Laurent Vivier
2007-02-21T16:07:58Z

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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
--
------------- Laurent.Vivier-6ktuUTfB/bM@public.gmane.org --------------
"Any sufficiently advanced technology is
indistinguishable from magic." - Arthur C. Clarke

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