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

[Thomas Pi]

After comparing some kernel code, I have found come really interesting
fact. I think the poor desktop responsiveness is affected by the changed
process scheduler (e.g. tickless kernel / high resolution timer ...) and
not by the disc scheduler. I have written a test program (sorry for the
dirty code), which enforces the problem and allows to measure it.

Here some fact. I have executed the tests in recovery mode (kernel
parameter single) once with 20 processes * 1.000.000 messages and once
with 100 processes * 100.000 messages. The result values are echo time
of ~80-90% of the messages / longest echo time and test duration.

CentOS
2.6.18-92.el5  -  20/1M  4µs / 1s / 38,4s   -   100/1k  4µs / 1s / 18,7s
Ubuntu 6.04 - 8.10
2.6.15-53  -  20/1M  3-33µs / 1s / 33,6s   -   100/1k  3-40µs / 1s / 17,7s
2.6.20-17  -  20/1M  3µs / 1s / 32s   -   100/1k  3-9µs / 1s / 16,0s
2.6.22-16  -  20/1M  3-4µs / 7s / 51,5s   -   100/1k  4µs / 1s / 25,9s
2.6.24-23  -  20/1M  53µs / 64s / 73ms   -   100/1k  77-250µs / 41ms / 32,0s
2.6.27-9  -  20/1M  120-200µs / 120ms / s   -   100/1k  500-1000µs / 1s / 84s

While executing the test with 100/1M under xorg/Gnome, the problem is
enforced. There are no problems on CentOS and Feisty. I could not test
it on Ubuntu 6.06. And had heavy responsiveness problems with Hardy,
Intrepid and Fedora 10. With 2.6.22 (installed in Feisty) the problem
sometimes occurs and sometimes not.

** Attachment added: "ProcessSchedulerTest.cpp"
   http://launchpadlibrarian.net/21115172/ProcessSchedulerTest.cpp

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