Subject: Re: fio rand read/write regression with 2.6.32-rc3
From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
To: Jens Axboe <jens.axboe@oracle.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
       Linus Torvalds <torvalds@linux-foundation.org>
In-Reply-To: <20091010080200.GO9228@kernel.dk>
References: <1255153724.25078.68.camel@ymzhang>
	 <20091010080117.GN9228@kernel.dk>  <20091010080200.GO9228@kernel.dk>
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Date: Sat, 10 Oct 2009 17:47:42 +0800
Message-Id: <1255168062.25078.79.camel@ymzhang>
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On Sat, 2009-10-10 at 10:02 +0200, Jens Axboe wrote:
> On Sat, Oct 10 2009, Jens Axboe wrote:
> > On Sat, Oct 10 2009, Zhang, Yanmin wrote:
> > > Comparing with 2.6.23-rc1's result, fio rand read write has regression
> > > on my 2*4 core stoakley machine (8GB memory) with a JBOD of 12 disks.
> > > 
> > > Every disk has 8 1-GB files. Start 8 sub-processes per disk and every
> > > process random chooses a file on the disk to do 36 times of file read or
> > > write on the file and then choose another file.
> > > 
> > > 
> > > fio_mmap_rand_read_4k regresion is about 35%.
> > 
> > Heh, I seem to recollect I told Linus that this would cost is 30-40%
> > performance. So not totally crazy.
> > 
> > So yes, this isn't hugely unexpected. If you send me your fio job files,
> > I'll try and see what I can do about it.
> 
> Oh, and can you check whether setting
> 
> /sys/block/sdX/queue/iosched/low_latency
> 
> to 0 for the involved devices makes the regression go away?
Echo 0 to low_latency makes the regression become less than 3%.


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