Re: [Qemu-devel] slow virtio network with vhost=on and multiple cores

[Jan Kiszka <jan.kiszka@web.de>]

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On 2012-11-06 12:24, Dietmar Maurer wrote:
>> On 2012-11-06 10:46, Dietmar Maurer wrote:
>>>>> This obviously breaks vhost when using multiple cores.
>>>>
>>>> With "obviously" you mean you already have a clue why?
>>>>
>>>> I'll try to reproduce.
>>>
>>> No, sorry - just meant the performance regression is obvious (factor 20 to
>> 40).
>>>
>>
>> OK. Did you try to bisect over qemu-kvm as well?
> 
> No (I thought that is the same code base?)

Already answered, though accidentally in private only: it is the same
code base now, but qemu-kvm has a different history and may contain
versions that didn't suffer from the issue.

Meanwhile I quickly tried to reproduce but didn't succeed so far
(>10GBit between host and guest with vhost=on and 2 guest cores).
However, I finally realized that we are talking about a pretty special
host kernel which I don't have around. I guess this is better dealt with
by Red Hat folks. Specifically, they should know what features that
kernel exposes and what it lacks.

Jan


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