Re: ext2/3 performance regression in 2.6 vs 2.4 for small interleaved writes

[Jon Burgess <lkml@jburgess.uklinux.net>]

Andrew Morton wrote:

>What filesytem was that with?
>  
>
I re-ran the tests again last night and founfd that I had made one 
mistake in my description.

The really poor results occured with the *ext3* filesystem, not ext2.

"mount" was telling me that the contents of /etc/fstab which was ext2 - 
but the kernel actually had it mounted it as ext3.

I think I might be able to give a little insight to the "0.34MB/s" and 
"0.48MB/s" numbers. I think these numbers closely match the theoretical 
performance rate when a single 4kB write occurs per disk rotation.

4kB * 5400RPM / 60 seconds = 360 kB/s
4kB * 7200RPM / 60 seconds = 480 kB/s

Perhaps the drives that I am running the test on do not have 
write-caching enabled.
By the time the first 4kB write has completed the drive may need to wait 
a complete rotation before it can do the next write. I don't think it 
quite explains the difference between ext2 and ext3. Any ideas?

Below are the resuls of ext2/ext3 tests on a new Seagate 80Gb SATA, 8MB 
Cache, model ST380023AS.
The ext3 results are a lot better, perhaps this drive has write caching 
enabled.

Num streams    |1      1      |2      2      |4       4
Filesystem     |Write  Read   |Write  Read   |Write   Read
------------------------------|--------------|--------------
Ext2           |40.17  43.07  |10.88  21.49  |10.13   11.41
ext3-journal   |16.06  42.24  | 7.56  16.28  | 7.17   11.25
ext3-ordered   |37.31  43.12  | 4.64  15.33  | 5.25   11.28
ext3-writeback |37.33  42.93  | 4.00  14.88  | 2.97   11.26


    Jon