Messages in this thread | | | From | Bill Davidsen <> | Subject | Re: Scheduler fairness problem on 2.6 series | Date | Thu, 12 Aug 2004 14:18:44 -0400 |
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Con Kolivas wrote: > 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.
There's a generalization which should confuse novice users... correctly used a timeout IS a debugging technique. Useful to detect when a peer has gone walkabout, as a common example.
Sounds as if the timeout is way too low here, however. Perhaps they are using it as poorly-done polling? In any case, not kernel misbehaviour.
-- -bill davidsen (davidsen@tmr.com) "The secret to procrastination is to put things off until the last possible moment - but no longer" -me - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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