Messages in this thread | | | Date | Sat, 13 Dec 2014 09:11:40 +0100 | From | Ingo Molnar <> | Subject | Re: frequent lockups in 3.18rc4 |
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* Mike Galbraith <umgwanakikbuti@gmail.com> wrote:
> On Tue, 2014-12-02 at 08:33 -0800, Linus Torvalds wrote: > > > Looking again at that patch (the commit message still doesn't strike > > me as wonderfully explanatory :^) makes me worry, though. > > > > Is that > > > > if (rq->skip_clock_update-- > 0) > > return; > > > > really right? If skip_clock_update was zero (normal), it now gets set > > to -1, which has its own specific meaning (see "force clock update" > > comment in kernel/sched/rt.c). Is that intentional? That seems insane. > > Yeah, it was intentional. Least lines. > > > Or should it be > > > > if (rq->skip_clock_update > 0) { > > rq->skip_clock_update = 0; > > return; > > } > > > > or what? Maybe there was a reason the patch never got applied even to -tip. > > Peterz was looking at corner case proofing the thing. Saving those > cycles has been entirely too annoying. > > https://lkml.org/lkml/2014/4/8/295
Hm, so that discussion died with:
https://lkml.org/lkml/2014/4/8/343
Did you ever get around to trying Peter's patch?
But ... I've yet to see rq_clock problems cause actual lockups. That's the main problem we have with its (un)robustness and why Peter created that rq_clock debug facility: bugs there cause latencies but no easily actionable symptoms, which are much harder to debug.
Thanks,
Ingo
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