Date: Sat, 10 Oct 2009 10:02:00 +0200
From: Jens Axboe <jens.axboe@oracle.com>
To: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
       Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: fio rand read/write regression with 2.6.32-rc3
Message-ID: <20091010080200.GO9228@kernel.dk>
References: <1255153724.25078.68.camel@ymzhang> <20091010080117.GN9228@kernel.dk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20091010080117.GN9228@kernel.dk>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1136
Lines: 32

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?

-- 
Jens Axboe

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/