[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] Very poor IO performance which looks like some design p
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] Very poor IO performance which looks like some design problem. |
Date: |
Sat, 11 Apr 2015 15:09:06 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
On 10/04/2015 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?
Use "aio=native,cache=none". If that's not enough, you'll need to use
XFS or a block device; ext4 suffers from spinlock contention on O_DIRECT
I/O.
Paolo