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

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


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