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Re: [Qemu-devel] Very poor IO performance which looks like some design p
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] Very poor IO performance which looks like some design problem. |
Date: |
Mon, 13 Apr 2015 09:45:46 +0800 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Fri, 04/10 22:38, ein wrote:
> Qemu creates more than 70 threads and everyone of them tries to write to
> disk, which results in:
> 1. High I/O time.
> 2. Large latency.
> 2. Poor sequential read/write speeds.
>
> When I limited number of cores, I guess I limited number of threads as
> well. That's why I got better numbers.
>
> I've tried to combine AIO native and thread setting with deadline
> scheduler. Native AIO was much more worse.
>
> The final question, is there any way to prevent Qemu for making so large
> number of processes when VM does only one sequential R/W operation?
aio=native will make QEMU only submit IO from the IO thread, so you shouldn't
see 70 threads with that. And that should usually be a better option for
performance.
Fam