Re: [ANNOUNCE] Native Linux KVM tool v2

From: Pekka Enberg
Date: Thu Jun 16 2011 - 03:33:32 EST

Hi Ingo,

On Thu, Jun 16, 2011 at 10:24 AM, Ingo Molnar <mingo@xxxxxxx> wrote:
>  - executing AIO in the vcpu thread eats up precious vcpu execution
>   time: combined QCOW2 throughput would be limited by a single
>   core's performance, and any time spent on QCOW2 processing would
>   not be spent running the guest CPU. (In such a model we certainly
>   couldnt do more intelligent, CPU-intense storage solutions like on
>   the fly compress/decompress of QCOW2 data.)

Most image formats have optional on-the-fly compression/decompression
so we'd need to keep the current I/O thread scheme anyway.

> I'd only consider KAIO it if it provides some *real* measurable
> performance advantage of at least 10% in some important usecase.
> A few percent probably wouldnt be worth it.

I've only been following AIO kernel development from the sidelines but
I really haven't seen any reports of significant gains over
read()/write() from a thread pool. Are there any such reports?

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