On Sat, Aug 11, 2007 at 12:50:08AM +0200, Roman Zippel wrote:
> Hi,
>
> On Fri, 10 Aug 2007, Ingo Molnar wrote:
>
> > achieve that. It probably wont make a real difference, but it's really
> > easy for you to send and it's still very useful when one tries to
> > eliminate possibilities and when one wants to concentrate on the
> > remaining possibilities alone.
>
> The thing I'm afraid about CFS is its possible unpredictability, which
> would make it hard to reproduce problems and we may end up with users with
> unexplainable weird problems. That's the main reason I'm trying so hard to
> push for a design discussion.
You may be interested by looking at the very early CFS versions. The design
was much more naive and understandable. After that, a lot of tricks have
been added to take into account a lot of uses and corner cases, which may
not help in understanding it globally.
> Just to give an idea here are two more examples of irregular behaviour,
> which are hopefully easier to reproduce.
>
> 1. Two simple busy loops, one of them is reniced to 15, according to my
> calculations the reniced task should get about 3.4% (1/(1.25^15+1)), but I
> get this:
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> 4433 roman 20 0 1532 300 244 R 99.2 0.2 5:05.51 l
> 4434 roman 35 15 1532 72 16 R 0.7 0.1 0:10.62 l
Could this be caused by typos in some tables like you have found in wmult ?
> OTOH upto nice level 12 I get what I expect.
>
> 2. If I start 20 busy loops, initially I see in top that every task gets
> 5% and time increments equally (as it should):
(...)
> But if I renice all of them to -15, the time every task gets is rather
> random:
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> 4492 roman 5 -15 1532 68 16 R 1.0 0.1 0:07.95 l
> 4491 roman 5 -15 1532 68 16 R 4.3 0.1 0:07.62 l
> 4490 roman 5 -15 1532 68 16 R 3.3 0.1 0:07.50 l
> 4489 roman 5 -15 1532 68 16 R 7.6 0.1 0:07.80 l
> 4488 roman 5 -15 1532 68 16 R 9.6 0.1 0:08.31 l
> 4487 roman 5 -15 1532 68 16 R 3.3 0.1 0:07.59 l
> 4486 roman 5 -15 1532 68 16 R 6.6 0.1 0:07.08 l
> 4485 roman 5 -15 1532 68 16 R 10.0 0.1 0:07.31 l
> 4484 roman 5 -15 1532 68 16 R 8.0 0.1 0:07.30 l
> 4483 roman 5 -15 1532 68 16 R 7.0 0.1 0:07.34 l
> 4482 roman 5 -15 1532 68 16 R 1.0 0.1 0:05.84 l
> 4481 roman 5 -15 1532 68 16 R 1.0 0.1 0:07.16 l
> 4480 roman 5 -15 1532 68 16 R 3.3 0.1 0:07.00 l
> 4479 roman 5 -15 1532 68 16 R 1.0 0.1 0:06.66 l
> 4478 roman 5 -15 1532 68 16 R 8.6 0.1 0:06.96 l
> 4477 roman 5 -15 1532 68 16 R 8.6 0.1 0:07.63 l
> 4476 roman 5 -15 1532 68 16 R 9.6 0.1 0:07.38 l
> 4475 roman 5 -15 1532 68 16 R 1.3 0.1 0:07.09 l
> 4474 roman 5 -15 1532 68 16 R 2.3 0.1 0:07.97 l
> 4473 roman 5 -15 1532 296 244 R 1.0 0.2 0:07.73 l
Do you see this only at -15, or starting with -15 and below ?
Willy
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