On Mon, 2008-01-28 at 09:50 +0100, Peter Zijlstra wrote: > On Sun, 2008-01-27 at 17:13 +0100, Michel Dänzer wrote: > > > In summary, there are two separate problems with similar symptoms, which > > had me confused at times: > > > > * With CONFIG_FAIR_USER_SCHED disabled, there are severe > > interactivity hickups with a niced CPU hog and top running. This > > started with commit 810e95ccd58d91369191aa4ecc9e6d4a10d8d0c8. > > The revert at the bottom causes the wakeup granularity to shrink for + > nice and to grow for - nice. That is, it becomes easier to preempt a + > nice task, and harder to preempt a - nice task.
Yeah, that matches my observations. :) > I think we originally had that; didn't comment it, forgot the reason > changed it because the units didn't match. Another reason might have > been the more difficult preemption of - nice tasks. That might - niced > tasks to cause horrible latencies - Ingo, any recollection? > > Are you perhaps running with a very low HZ (HZ=100)? (If wakeup > preemption fails, tick preemption will take over). I haven't had it below 250 since that became an option, and I'm currently at 1000 (and NO_HZ, but disabling that didn't seem to make a difference). > Also, could you try lowering: > /proc/sys/kernel/sched_wakeup_granularity_ns Will try. > > * With CONFIG_FAIR_USER_SCHED enabled, X becomes basically > > unusable with a niced CPU hog, with or without top running. I > > don't know when this started, possibly when this option was > > first introduced. > > Srivatsa found an issue that might explain the very bad behaviour under > group scheduling. But I gather you're not at all interested in this > feature? That's right, but it's good to hear you have a lead there as well, and if you can't find any interested testers, let me know and I'll try. -- Earthling Michel Dänzer | http://tungstengraphics.com Libre software enthusiast | Debian, X and DRI developer _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
