From: Brian Candler <B.Candler@pobox.com>
To: Dave Chinner <david@fromorbit.com>
Cc: xfs@oss.sgi.com
Subject: Re: Performance problem - reads slower than writes
Date: Tue, 31 Jan 2012 21:35:22 +0000 [thread overview]
Message-ID: <20120131213522.GA47420@nsrc.org> (raw)
In-Reply-To: <20120131200635.GI9090@dastard>
On Wed, Feb 01, 2012 at 07:06:35AM +1100, Dave Chinner wrote:
> The number of IOs does not equal the number of seeks. Two adjacent,
> sequential IOs issued serially will show up as two IOs, even though
> there was no seek in between. Especially if the files are large
> enough that readahead tops out (500-800k is large enough for this as
> readahead maximum is 128k by default). So it might be taking 3-4
> IOs just to read the file data.
Ah. And if the IOs are not stacked up, then the platter has to rotate nearly
a whole turn to perform the next one.
> > So the next thing I'd have to do is to try to get a trace of the I/O
> > operations being performed, and I don't know how to do that.
>
> blktrace/blkparse or seekwatcher.
Excellent, just what I wanted. I've made a start with this and will report
back.
Many thanks for the help and pointers you have provided.
Regards,
Brian.
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prev parent reply other threads:[~2012-01-31 21:35 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-30 22:00 Performance problem - reads slower than writes Brian Candler
2012-01-31 2:05 ` Dave Chinner
2012-01-31 10:31 ` Brian Candler
2012-01-31 14:16 ` Brian Candler
2012-01-31 20:25 ` Dave Chinner
2012-02-01 7:29 ` Stan Hoeppner
2012-02-03 18:47 ` Brian Candler
2012-02-03 19:03 ` Christoph Hellwig
2012-02-03 21:01 ` Brian Candler
2012-02-03 21:17 ` Brian Candler
2012-02-05 22:50 ` Dave Chinner
2012-02-05 22:43 ` Dave Chinner
2012-01-31 14:52 ` Christoph Hellwig
2012-01-31 21:52 ` Brian Candler
2012-02-01 0:50 ` Raghavendra D Prabhu
2012-02-01 3:59 ` Dave Chinner
2012-02-03 11:54 ` Brian Candler
2012-02-03 19:42 ` Stan Hoeppner
2012-02-03 22:10 ` Brian Candler
2012-02-04 9:59 ` Stan Hoeppner
2012-02-04 11:24 ` Brian Candler
2012-02-04 12:49 ` Stan Hoeppner
2012-02-04 20:04 ` Brian Candler
2012-02-04 20:44 ` Joe Landman
2012-02-06 10:40 ` Brian Candler
2012-02-07 17:30 ` Brian Candler
2012-02-05 5:16 ` Stan Hoeppner
2012-02-05 9:05 ` Brian Candler
2012-01-31 20:06 ` Dave Chinner
2012-01-31 21:35 ` Brian Candler [this message]
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