Re: call for more SD versus CFS comparisons (was: Re: [ck] Mainline plans)

From: Tobias Gerschner
Date: Tue Jun 12 2007 - 03:39:37 EST

2007/6/12, Miguel Figueiredo <elmig@xxxxxxxxxxxx>:
Hi all,

some results based on massing_intr.c by Satoru, can be found on

2007/6/12, Miguel Figueiredo <elmig@xxxxxxxxxxxx>:
Hi all,

some results based on massing_intr.c by Satoru, can be found on


Thanks for this reminder. I am gonna provide similar results if wanted
and useful for any dev.

However I took massiv_intr.c for a slightly different approach of
testing. The sole focus was responsiveness / (usable responsiveness
)of the desktop from the pov of an user.

I used massive_intr.c to bring the system to a state of lacking
usability ( overloaded system ) .

The setup was as follow:

mergedfb 2 monitors

Left desktop was displaying a music video playback using kaffeine /
xine at 100 % size. Right
Desktop had Firefox with 4 Tabs open 2 were text, 2 were graphical .

I did run massive_intr.c for 60 secs with increasing nproc (
10,20,30,40,50,60) waiting for effects.

Below a small table of the results

nproc , usability result

10 , serious frame drops , Firefox hardly recognizes clicked links,
but still usable
20 - 30, usability loss ( somehow under cfs firefox never finished
user requests like displaying web pages or opening new pages , no
feedback anymore, sudden changes on the desktop )
40 , sound skipping

nproc , usability result

10 - 20 , fine
30 - 50 , video frame drops , stair effect in playback
60 , unusable delay for responding to user actions ( clicking links ,
switching tabs )
70 , sound skipping

I know that this is still highly subjective but I tried to describe
the test procedure to make it as repeatable and simple as possible.
Furthermore tried to scale the user experience into numbers. I won't
even attempt to interpret those results but from an user point of view
the answer is crystal clear. It still remains -ck
. I performed this test 3 times and results are clearly the same.

As a sidenote . CK / SD seemed to be far more scalable in general. I
started designing a bit more complicated test scenario involving more
applications and opening new applications in a 2 minute timeframe. I
did this using -ck .

Once I booted into -cfs-v16 I realized that this test case was useless
because that test could simply not be performed because -cfs-v16 did
not even closely scale that well as -ck did.

I'll keep testing both schedulers ... .

Input, questions and feedback regarding the testing method are highly

The output of massive_intr can be found here :

kind regards

Tobias Gerschner
Member of Board of Yoper Linux Ltd. NZ

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