Re: [BUG] scheduler: strange behavor with massive interactive processes

[Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>]

Hi Ingo,

> > > Hi Ingo and all,
> > > 
> > > When I was executing massive interactive processes, I found that some 
> > > of them occupy CPU time and the others hardly run.
> > 
> > yeah.
> > 
> > > I also attach the test program which easily recreates this problem.
> > 
> > thanks, this is really helpful - does the patch below improve the 
> > situation?

I tested your patch and it seems to work well.

Test environment
================

 - kernel: 2.6.21-rc5 with or without Ingo's patch
 - others: same as my initial mail except for omitting nice 19 cases

Result (without Ingo's patch)
=============================

  +---------+-----------+------+------+------+--------+
  |   # of  |   # of    | avg  | max  | min  |  stdev |
  |   CPUs  | processes | (*1) | (*2) | (*3) |  (*4)  |
  +---------+-----------+------+------+------+--------+
  | 1(i386) |       200 |  162 | 8258 |    1 |   1113 |
  +---------+-----------+------+------+------+--------+
  |         |           |  378 | 9314 |    2 |   1421 |
  | 2(ia64) |       400 +------+------+------+--------+
  |         |           |  189 |12544 |    1 |   1443 |
  +---------+-----------+------+------+------+--------+

  *1) average number of loops among all processes
  *2) maximum number of loops among all processes
  *3) minimum number of loops among all processes
  *4) standard deviation

Result (with Ingo's patch)
==========================

  +---------+-----------+------+------+------+--------+
  |   # of  |   # of    | avg  | max  | min  |  stdev |
  |   CPUs  | processes |      |      |      |        |
  +---------+-----------+------+------+------+--------+
  | 1(i386) |       200 |  153 |  232 |  128 |   7.67 |
  +---------+-----------+------+------+------+--------+
  |         |           |  376 |  451 |  291 |   17.6 |
  | 2(ia64) |       400 +------+------+------+--------+
  |         |           |  188 |  236 |  137 |   14.5 |
  +---------+-----------+------+------+------+--------+

Although it is not perfectly fair, it is certain that this patch really improve
the situation in dramatic form. Thank you very much!

Satoru