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Date: Fri, 21 Sep 2007 10:40:29 +1000 From: David Chinner <dgc@....com> To: Ramon Chimeno <ramon.chimeno@...il.com> Cc: linux-kernel@...r.kernel.org Subject: Re: Disk I/O degraded performance On Wed, Sep 19, 2007 at 10:09:12PM +0200, Ramon Chimeno wrote: > Hi all > > I migrated one of my server from kernel 2.6.18 to the latest 2.6.22 > and I experienced lower disk performance for processes that open file > with the O_DIRECT flag. > > I did a very simple test program that opens two files with O_DIRECT > flag and reads the files to end. I monitored the time spent to read > the files and I have ~ 40% of difference between 2.6.18 and 2.6.22. > > For information, the files are stored on a XFS partition which is part > of a software raid-5 block device (the raid-5 is made with 3 SATA > drives). Start by eliminating the filesystem. i.e. run the same test using different offsets on the raw device (e.g. seek one fd a few gigabytes further into the disk than the other then start reading). Also, you might want to check that you are comparing apples to apples; are the two files you used in each test the same? If not, are they all unfragmented, in the same AGs (i.e. all on the same area of disk as there's a 2x speed difference betweem the inner and outer edges), etc.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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