[Bug 131094] Re: Heavy Disk I/O harms desktop responsiveness

[Paulo J. S. Silva]

Did anyone try koala alpha 3?

I did and have some interesting behavior.

My machine (a intel motherboard with a G33 chipset) and Core 2 Duo E6600
processor. It has 2 SATA drives under AHCI and I use a 64bit kernel.

I can easily reproduce the problem using the fsync-tester program that you can get in the kernel bug #12309 (http://bugzilla.kernel.org/show_bug.cgi?id=12309). All I need to do is to run the program with a dd that creates 
very large file with the command line:

dd if=/dev/zero of=./bigfile bs=1M count=15000 & ./fsync-tester

In jaunty (ext3) the desktop becomes unresponsive right away. The times
given by fsync-tester look like:

fsync time: 0.5422
fsync time: 6.3691
fsync time: 8.5983
fsync time: 0.7820
fsync time: 0.7695
fsync time: 4.6577
fsync time: 5.6024
fsync time: 9.4238
fsync time: 10.8609

I tried some variations of koala. Here are my findings:

1) 64bit Koala in default configuration (ext4).

The desktop is more responsive, but not really good yet. The fsync-
tester gives:

fsync time: 0.1351
fsync time: 0.9104
fsync time: 9.1311
fsync time: 1.9133
fsync time: 11.9529
fsync time: 1.6751
fsync time: 2.7171
fsync time: 8.4801

So the better responsiveness is not related to the fsync times, probably it is related to other
changes in the kernel. There is no clear change if I go from turn AHCI off in the bios.

2) If I change the journal mode to writeback, the fsync times improve a
lot (and the responsiveness improve):

fsync time: 0.0781
fsync time: 0.0581
fsync time: 1.7040
fsync time: 1.4743
fsync time: 1.5957
fsync time: 1.7751
fsync time: 1.9164
fsync time: 1.4886
fsync time: 1.3991
fsync time: 1.8332

3) If on the other hand, I use a i386 kernel with the default ordered
mode the times are also much better (as good as writeback + amd64):

fsync time: 0.0677
fsync time: 3.8825
fsync time: 1.4467
fsync time: 2.7759
fsync time: 1.5819
fsync time: 3.2423
fsync time: 3.4318
fsync time: 1.5432
fsync time: 1.3225

4) i386 + writeback gets a little better:

fsync time: 0.0946
fsync time: 1.3528
fsync time: 1.4029
fsync time: 1.3787
fsync time: 1.0880
fsync time: 1.2656
fsync time: 0.9047
fsync time: 0.8842
fsync time: 0.8008
fsync time: 1.4933
fsync time: 1.3645

(There are know 3s delays as above)

5) Now comes the interesting surprise. If I install amd64 koala using ext3 with its default mode (which I think is 
writeback, but I am not sure). I get very good responsiveness and times:

fsync time: 0.0329
fsync time: 0.0156
fsync time: 0.2369
fsync time: 0.1274
fsync time: 0.2285
fsync time: 0.2196
fsync time: 0.2563
fsync time: 0.2147
fsync time: 0.2968
fsync time: 0.2602
fsync time: 0.1131
fsync time: 0.2348

I didn't try i386+ext3. I ran out of time and patience :-)

So, in my computer the problem seems to be related with many factors:
amd64 X i386,  writeback X ordered mode, and ext4 X ext3.

It would be very interesting if anyone can reproduce my little
experiment.

And remember, if you are annoyed by this bug you may want to stick with
ext3 in koala for now.

-- 
Heavy Disk I/O harms desktop responsiveness
https://bugs.launchpad.net/bugs/131094
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