On Thu, 6 Mar 2014 12:58:25 +0100 Peter Zijlstra <pet...@infradead.org> wrote:
> On Wed, Mar 05, 2014 at 11:29:31PM -0500, Steven Rostedt wrote: > > I decided to run my tests on linux-next, and my wakeup_rt tracer was > > broken. After running a bisect, I found that the problem commit was: > > > > linux-next commit c365c292d059 > > "sched: Consider pi boosting in setscheduler()" > > > > And the reason the wake_rt tracer test was failing, was because it had > > no RT task to trace. I first noticed this when running with > > sched_switch event and saw that my RT task still had normal SCHED_OTHER > > priority. Looking at the problem commit, I found: > > > > - p->normal_prio = normal_prio(p); > > - p->prio = rt_mutex_getprio(p); > > > > With no > > > > + p->normal_prio = normal_prio(p); > > + p->prio = rt_mutex_getprio(p); > > > > Reading what the commit is suppose to do, I realize that the p->prio > > can't be set if the task is boosted with a higher prio, but the > > p->normal_prio still needs to be set regardless, otherwise, when the > > task is deboosted, it wont get the new priority. > > > > The p->prio has to be set before "check_class_changed()" is called, > > otherwise the class wont be changed. > > So Juri had a different patch for this problem: > > http://lkml.kernel.org/r/20140301191838.d15d03112b2598a671dac...@gmail.com > > > Signed-off-by: Steven Rostedt <rost...@goodmis.org> > > --- > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index 4600bca..b1cc871 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -3198,6 +3198,7 @@ static void __setscheduler_params(struct task_struct > > *p, > > * getparam()/getattr() don't report silly values for !rt tasks. > > */ > > p->rt_priority = attr->sched_priority; > > + p->normal_prio = normal_prio(p); > > set_load_weight(p); > > } > > Now; if I'm reading things right, normal_prio is the unboosted priority > of a task. And we should indeed keep setting that, otherwise the unboost > doesn't know where it should go. > > Juri put that in __setscheduler(), but I think that's wrong because the > rt_mutex_check_prio() case in __sched_setscheduler() still needs to > update this. > Oh, right. Missed that. > > @@ -3207,6 +3208,8 @@ static void __setscheduler(struct rq *rq, struct > > task_struct *p, > > { > > __setscheduler_params(p, attr); > > > > + p->prio = rt_mutex_getprio(p); > > + > > if (dl_prio(p->prio)) > > p->sched_class = &dl_sched_class; > > else if (rt_prio(p->prio)) > > > > And when we call this we're sure to not be boosted; so this is > effectively the same as Juri has: > > p->prio = p->normal_prio = normal_prio(p) > > Seeing how rt_mutex_getprio() and normal_prio() are the same under these > conditions. > > Yes. I think you can go with p->prio = p->normal_prio and save a few checks in rt_mutex_getprio(). Thanks, - Juri -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
