Comment 80 for bug 620074

Created attachment 19920
ext3 and ext4 comparison with patched and unpatched kernel

Here some more results. I could gain or loose some latency by different kernel settings. In 2.6.20 I could reproduceable loose 10ms, which makes a decrease of 25% of average latency. But it makes no difference in the desktop responsiveness.

I have tested the 2.6.28 kernel as patched ( http://bugzilla.kernel.org/attachment.cgi?id=19866 ) and unpatched kernel with ext3 and ext4 with exactly the same kernel settings. My test system is installed on a ext3 partition, the tests are executed on a extra ext3 or ext4 (on the slower one) partition on the same hard drive. The write performance on ext4 is now at 45MB/s instead of 35MB/s (ext3).

The destop responsiveness on the ext4 test with the patched version decreases extremely. While copying a 10gig file from ext4 to ext4, there is nerby no problems with the unpatched kernel. While using the patched kernel, the system becomes unuseable. With ext3 there is a little responsiveness improve with the patched kernel. But it can be coincidence, as I have no exact test for desktop responsiveness.

But while copying the 10gig file on ext4 and compiling the kernel, my system becomes unusable with the unpatched kernel too. There are freezes for >20 seconds, while access the menu in applications the first time.
You can easly simulate this behaviour by executing the following compression for every core.

bzip2 -9 -c /dev/urandom >/dev/null &

And the average latencies of the last four tests.

                             min maxa avg stdev
2.6.28 unpatched ext3 11.24 181.20 62.35 86.15
2.6.28 patched ext3 10.82 175.93 62.18 83.89
2.6.28 unpatched ext4 6.90 396.17 132.52 213.18
2.6.28 patched ext4 6.85 2078.93 707.26 1006.74