Messages in this thread | | | Date | Wed, 26 Aug 2009 11:52:48 -0700 | From | Darren Hart <> | Subject | Re: [RFC][PATCH -rt] sched: fully ignore RT tasks for CFS load-balancing |
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Peter Zijlstra wrote: > Since -rt runs IRQs and SoftIRQs as RT tasks and load-balancing is done > from softirq context, there is always at least one RT task (and very > likely multiple) running when we balance. > > The current (and totally broken) interaction between RT tasks and CFS > load-balancing makes it so that we'll try to evacuate a significant > amount of tasks due to RT tasks being runnable. > > Solve this in another broken way by not accounting RT tasks at all. > > This will likely break another class of cases, but until we can properly > fix this, we might as well do this.
Peter,
Do we know why this became a problem lately? I don't recall seeing load balancing issues like this way back around 2.6.21 or 22 when CFS was released. Is the cpu_load stuff fairly recent?
-- Darren
> > Chucked-on-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > --- > kernel/sched_rt.c | 4 ---- > 1 files changed, 0 insertions(+), 4 deletions(-) > > diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c > index adcbc68..385d31f 100644 > --- a/kernel/sched_rt.c > +++ b/kernel/sched_rt.c > @@ -926,8 +926,6 @@ static void enqueue_task_rt(struct rq *rq, struct > task_struct *p, int wakeup) > > if (!task_current(rq, p) && p->rt.nr_cpus_allowed > 1) > enqueue_pushable_task(rq, p); > - > - inc_cpu_load(rq, p->se.load.weight); > } > > static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int > sleep) > @@ -942,8 +940,6 @@ static void dequeue_task_rt(struct rq *rq, struct > task_struct *p, int sleep) > dequeue_rt_entity(rt_se); > > dequeue_pushable_task(rq, p); > - > - dec_cpu_load(rq, p->se.load.weight); > } > > /* > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
-- Darren Hart IBM Linux Technology Center Real-Time Linux Team
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