linux-ext4 - ext3 sequential read performance (~20%) degrade

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Date:	Thu, 14 Sep 2006 16:36:12 -0700
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	akpm@...l.org, sct@...hat.com
Cc:	ext4 <linux-ext4@...r.kernel.org>
Subject: ext3 sequential read performance (~20%) degrade

Hi Andrew,

I have been working on tracking down ~20% performance degrade for
sequential read performance for ext3. 

Finally narrowed it down to get_blocks() support. If I force
ext3_get_blocks_handle() to always return 1 block - I get better
IO rate. I did all the usual stuff, tracked down requests, traced
blocksizes, looked at readahead code, looked at mpage_readpages()
etc.. I still can't figure out how to explain the degrade..

Any suggestions on how to track it down.

Thanks,
Badari

# cat iotest
mount /dev/sdb2 /mnt/tmp
time dd if=/mnt/tmp/testfile of=/dev/null bs=4k count=1048576
umount /mnt/tmp

2.6.18-rc6: (multiblock):

# ./iotest
1048576+0 records in
1048576+0 records out
4294967296 bytes (4.3 GB) copied, 75.2654 seconds, 57.1 MB/s

real    1m15.282s
user    0m0.248s
sys     0m4.292s

2.6.18-rc6 (force single block in ext3_get_blocks_handle():

# ./iotest
./iotest
1048576+0 records in
1048576+0 records out
4294967296 bytes (4.3 GB) copied, 62.9472 seconds, 68.2 MB/s

real    1m2.976s
user    0m0.268s
sys     0m4.280s

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