Re: Scheduler fairness problem on 2.6 series

[Con Kolivas <kernel@kolivas.org>]

[-- Attachment #1: Type: text/plain, Size: 1404 bytes --]

Prakash K. Cheemplavam wrote:
> |
> | I don't think it is the overhead. I rather think the way the kernel
> | schedulers gives mpich and the cpu bound program  resources is unfair.
> 
> Well, I don't know whether it helps, but I ran a profiler and these are
> the functions which cause so much wasted CPU cycles when running 16
> processes of my example with mpich:
> 
> 124910    9.8170  vmlinux                  tcp_poll
> 123356    9.6949  vmlinux                  sys_select
> 85634     6.7302  vmlinux                  do_select
> 71858     5.6475  vmlinux                  sysenter_past_esp
> 62093     4.8801  vmlinux                  kfree
> 51658     4.0600  vmlinux                  __copy_to_user_ll
> 37495     2.9468  vmlinux                  max_select_fd
> 36949     2.9039  vmlinux                  __kmalloc
> 22700     1.7841  vmlinux                  __copy_from_user_ll
> 14587     1.1464  vmlinux                  do_gettimeofday
> 
> Is anything scheduler related?

No

It looks like your select timeouts are too short and when the cpu load 
goes up they repeatedly timeout wasting cpu cycles.
I quote from `man select_tut` under the section SELECT LAW:

1. You should always try use select without a timeout. Your program
  should have nothing to do if there is no  data  available.  Code
  that  depends  on timeouts is not usually portable and difficult
  to debug.

Cheers,
Con

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 256 bytes --]