Messages in this thread | | | Subject | Re: frequent lockups in 3.18rc4 | From | Mike Galbraith <> | Date | Sat, 13 Dec 2014 10:57:42 +0100 |
| |
On Sat, 2014-12-13 at 09:11 +0100, Ingo Molnar wrote: > * 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?
I couldn't plug it into the production -ENOBOOT IO beasts from hell, but did run it on my little desktop a bit. > 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.
If watchdog gets credit for zillion disk detection time, it can end up throttled for what is effectively forever.
-Mike
| |