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Re: [Qemu-devel] Question about posixaio thread number.
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] Question about posixaio thread number. |
Date: |
Wed, 3 Aug 2011 08:23:46 +0100 |
On Wed, Aug 3, 2011 at 6:19 AM, Gui Jianfeng <address@hidden> wrote:
> When i did some io tests in Guest say dd like
> dd if=/dev/zero oflag=direct of=/mnt/sdb1/date.img bs=4k count=262114
>
> qemu will start one or several threads to perform IO requests.
>
> It seems qemu makes use of its own posixaio. I'm wondering how qemu
> decides how many threads should be created to perform io operation?
Look at posix-aio-compat.c.
If a new request comes in and there is no idle thread around, a new
thread will be spawned up to a maximum limit.
When you run a synchronous I/O workload like dd(1), expect to see only
1 or 2 aio worker threads. If the workload is multithreaded, expect
to see many (depending on the guest's queue depth).
Stefan