From: Stefan Hajnoczi <stefanha@gmail.com>
To: cauchy-love <cauchy-love@163.com>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] Greate difference of disk I/O performance for guest on Qemu-2.30 of CentOS.
Date: Fri, 19 Jun 2015 16:24:58 +0100 [thread overview]
Message-ID: <20150619152458.GC20966@stefanha-thinkpad.redhat.com> (raw)
In-Reply-To: <6bc2d8e.1e4b.14e0942385e.Coremail.cauchy-love@163.com>
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On Fri, Jun 19, 2015 at 08:40:11AM +0800, cauchy-love wrote:
>
> the iozone command line is:
> ./iozone -i 0 -i 1 -f ./iotmp -Rab ./iotmp.xls -g 8G -n 4G -c
>
> The problem is why the performance difference is so big for different linux kernels. The guest's io performance test is by both FTP tools and raw write, which demonstrate the much lower performance of Centos 7 (1/10 of that on Centos 6.5). And how can I debug this problem?
You are missing the -I command-line option for O_DIRECT.
When you run without -I you are not benchmarking just disk I/O but also
page cache performance, which varies depending on the amount of RAM
available. This means you cannot compare guest results with host
results.
Stefan
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next prev parent reply other threads:[~2015-06-19 15:25 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-15 13:14 [Qemu-devel] Greate difference of disk I/O performance for guest on Qemu-2.30 of CentOS cauchy-love
2015-06-16 13:05 ` Stefan Hajnoczi
2015-06-19 0:40 ` cauchy-love
2015-06-19 15:24 ` Stefan Hajnoczi [this message]
2015-06-19 1:03 ` cauchy-love
2015-06-19 8:37 ` Paolo Bonzini
2015-06-23 3:22 ` cauchy-love
[not found] ` <5ec70e6c.267de.14e257e00ab.Coremail.cauchy-love@163.com>
[not found] ` <558AA072.3080507@redhat.com>
2015-06-24 12:31 ` cauchy-love
2015-06-24 12:32 ` Paolo Bonzini
2015-06-24 12:50 ` cauchy-love
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