Messages in this thread | | | Subject | Re: [PATCH] a patch to fix the cpu-offline-online problem caused by pm_idle | From | Peter Zijlstra <> | Date | Mon, 31 Jan 2011 11:16:46 +0100 |
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On Sun, 2011-01-30 at 22:26 -0500, Luming Yu wrote:
> > Guessing is totally the wrong thing when you're sending stuff upstream, > > esp ugly patches such as this. .32 is more than a year old, anything > > could have happened. > > Ok. the default upstream kernel seems to have NMI watchdog disabled?
Then enable it already, its a whole CONFIG option away..
> It's not working because of NMI watchdog. If you ignore NMI watchdog, > then I guess it works but just slow..
Don't guess, test it dammit. And then figure out why it triggers, I haven't seen _anything_ that would cause it to trigger, nor a sane explanation for your patch.
> > Ok, so one IPI costs 50-100 us, even with 64 cpu, that's at most 6.4ms > > nowhere near enough to trigger the NMI watchdog. So what does go wrong? > > Good question! > But we also can't forget there were large latency from C3.
Not 60+ seconds large I hope, I know NHM-EX has some suckage, but surely not that bad?
> And I guess some reschedule ticks get lost to kick some CPUs out of > idle due to the side effects of the CPU PM feature. if use nohz=off, > everything seems to just work. > Yes, I agree we need to dig it out either. > But it's kind of combination problem between the special stop_machine > context and CPU power management...
Yeah, so? Also, incidentally, stop-machine got a rewrite around .35 and again significant changes in .37, so please do test mainline and not your dinosaur.
> > Yeah, what are you smoking? Why do you wreck perfectly fine code for one > > backward ass piece of hardware. > > Just make things less complex...
But its wrong, it very clearly works around a real problem, don't ever do that, fix the problem!
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