Messages in this thread | | | Subject | Re: 2.6.21-rc1: known regressions (v2) (part 2) | From | Mike Galbraith <> | Date | Tue, 27 Feb 2007 09:54:13 +0100 |
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On Tue, 2007-02-27 at 09:33 +0100, Ingo Molnar wrote: > * Michal Piotrowski <michal.k.k.piotrowski@gmail.com> wrote: > > > Thomas Gleixner napisał(a): > > > Adrian, > > > > > > On Mon, 2007-02-26 at 23:05 +0100, Adrian Bunk wrote: > > >> Subject : kernel BUG at kernel/time/tick-sched.c:168 (CONFIG_NO_HZ) > > >> References : http://lkml.org/lkml/2007/2/16/346 > > >> Submitter : Michal Piotrowski <michal.k.k.piotrowski@gmail.com> > > >> Handled-By : Thomas Gleixner <tglx@linutronix.de> > > >> Status : problem is being debugged > > > > > > The BUG_ON() was replaced by a warning printk(). The BUG_ON() exposed a > > > problem with the SMT scheduler. See below. > > > > > >> Subject : BUG: soft lockup detected on CPU#0 > > >> NOHZ: local_softirq_pending 20 (SMT scheduler) > > >> References : http://lkml.org/lkml/2007/2/20/257 > > >> Submitter : Michal Piotrowski <michal.k.k.piotrowski@gmail.com> > > >> Handled-By : Thomas Gleixner <tglx@linutronix.de> > > >> Ingo Molnar <mingo@elte.hu> > > >> Status : problem is being debugged > > > > > > Patch available, not confirmed yet. > > > > > > > I can confirm that the bug is fixed (over 20 hours of testing should > > be enough). > > thanks alot! I think this thing was a long-term performance/latency > regression in HT scheduling as well.
Agreed.
I was recently looking at that spot because I found that niced tasks were taking latency hits, and disabled it, which helped a bunch. I also can't understand why it would be OK to interleave a normal task with an RT task sometimes, but not others.. that's meaningless to the RT task.
IMHO, SMT scheduling should be a buyer beware thing. Maximizing your core utilization comes at a price, but so does disabling it, so I think letting the user decide what he wants is the right thing to do.
-Mike
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