linux-kernel - Re: 2.6.29.1 vs 2.6.27.21 ext4 performance problem

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Message-ID: <20090410163620.GA14814@mit.edu>
Date:	Fri, 10 Apr 2009 12:36:20 -0400
From:	Theodore Tso <tytso@....edu>
To:	"Alexander V. Lukyanov" <lav@....ru>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: 2.6.29.1 vs 2.6.27.21 ext4 performance problem

On Fri, Apr 10, 2009 at 07:12:35PM +0400, Alexander V. Lukyanov wrote:
> I have a server that is busy reading and writing several disks with
> ext4 fs.  After booting 2.6.29.1 kernel I have noticed significant
> increase in read rate.  I measure the read rate using a script which
> reads sysfs byte and access counts and calculates average per
> second.

Without knowing exactly what your workload is, it's hard to say for
sure.  One of the things which did go in after 2.6.27 was inode table
readahead.  The intent is to actually improve performance, although at
least initially it might mean a bit more I/O activity.

Does the differences go away if you do echo 0 into
/sys/fs/ext4/<dev>/inode_readahead_blks?

Are you seeing an increase in time, or decrease in transactions per
second, or just that there is is an increase in read rates?

	   	     	      	    	     - Ted
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