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Date: Wed, 3 Aug 2011 11:45:33 -0400
From: Vivek Goyal <vgoyal@redhat.com>
To: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Cc: Shaohua Li <shli@kernel.org>, Jens Axboe <jaxboe@fusionio.com>,
        linux-kernel@vger.kernel.org
Subject: Re: fio posixaio performance problem
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On Wed, Aug 03, 2011 at 05:48:54PM +0800, Gui Jianfeng wrote:
> On 2011-8-3 16:22, Shaohua Li wrote:
> > 2011/8/3 Gui Jianfeng <guijianfeng@cn.fujitsu.com>:
> >> On 2011-8-3 15:38, Shaohua Li wrote:
> >>> 2011/8/3 Gui Jianfeng <guijianfeng@cn.fujitsu.com>:
> >>>> Hi,
> >>>>
> >>>> I ran a fio test to simulate qemu-kvm io behaviour.
> >>>> When job number is greater than 2, IO performance is
> >>>> really bad.
> >>>>
> >>>> 1 thread: aggrb=15,129KB/s
> >>>> 4 thread: aggrb=1,049KB/s
> >>>>
> >>>> Kernel: lastest upstream
> >>>>
> >>>> Any idea?
> >>>>
> >>>> ---
> >>>> [global]
> >>>> runtime=30
> >>>> time_based=1
> >>>> size=1G
> >>>> group_reporting=1
> >>>> ioengine=posixaio
> >>>> exec_prerun='echo 3 > /proc/sys/vm/drop_caches'
> >>>> thread=1
> >>>>
> >>>> [kvmio-1]
> >>>> description=kvmio-1
> >>>> numjobs=4
> >>>> rw=write
> >>>> bs=4k
> >>>> direct=1
> >>>> filename=/mnt/sda4/1G.img
> >>> Hmm, the test runs always about 15M/s at my side regardless how many threads.
> >>
> >> CFQ？
> > yes.
> > 
> >> what's the slice_idle value?
> > default value. I didn't change it.
> 
> Hmm, I use a sata disk, and can reproduce this bug every time...

Do you have blktrace of run with 4 jobs?

Thanks
Vivek