Re: Scheduler fairness problem on 2.6 series

From: Prakash K. Cheemplavam
Date: Thu Aug 12 2004 - 03:09:27 EST


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Con Kolivas wrote:
| Prakash K. Cheemplavam wrote:
|
|> 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
|>
| 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.
|

Thanks for your explanation. I cannot do anything about it, as it is
mpich related. So I'll ask them if they could change its behaviour a bit
so that it eats less CPU on a single CPU machine.

Cheers,

Prakash
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