Messages in this thread | | | Date | Wed, 4 Mar 2020 15:28:20 +0000 | From | Qais Yousef <> | Subject | Re: [PATCH v3 4/6] sched/rt: Allow pulling unfitting task |
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On 03/04/20 22:52, Tao Zhou wrote: > Hi Qais, > > On Mon, Mar 02, 2020 at 01:27:19PM +0000, Qais Yousef wrote: > > When implemented RT Capacity Awareness; the logic was done such that if > > a task was running on a fitting CPU, then it was sticky and we would try > > our best to keep it there. > > > > But as Steve suggested, to adhere to the strict priority rules of RT > > class; allow pulling an RT task to unfitting CPU to ensure it gets a > > chance to run ASAP. > > > > Suggested-by: Steven Rostedt <rostedt@goodmis.org> > > Fixes: 804d402fb6f6 ("sched/rt: Make RT capacity-aware") > > LINK: https://lore.kernel.org/lkml/20200203111451.0d1da58f@oasis.local.home/ > > Signed-off-by: Qais Yousef <qais.yousef@arm.com> > > --- > > kernel/sched/rt.c | 3 +-- > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > > index 3071c8612c03..e79a23ad4a93 100644 > > --- a/kernel/sched/rt.c > > +++ b/kernel/sched/rt.c > > @@ -1656,8 +1656,7 @@ static void put_prev_task_rt(struct rq *rq, struct task_struct *p) > > static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu) > > { > > if (!task_running(rq, p) && > > - cpumask_test_cpu(cpu, p->cpus_ptr) && > > - rt_task_fits_capacity(p, cpu)) > > + cpumask_test_cpu(cpu, p->cpus_ptr)) > > return 1; > > > > return 0; > > -- > > 2.17.1 > > > > How about using a rt_cap_overloaded(like rt_overloaded) to indicate the > cpu is overloaded because a RT task is on unfit CPU. And use stop_one_cpu > to do in this case.
We have explored a variation of this (without using the stop_one_cpu) in v2
https://lore.kernel.org/lkml/20200223184001.14248-6-qais.yousef@arm.com/
I might still consider this in the future. But I think I need to do better analysis of the cost-benefit here before pushing further for that.
I'm not keen on stopping a running task as well, not yet at least.
> > IIRC, HAVE_RT_PUSH_IPI do not select the specific cpu to do the > push because the complex there. When RT cap join in, i don't know it > is need to select the specific unfit CPU or rt overloaded CPU in what > order is a choice.
I'm not sure I understood you completely here.
I think the patch above dealt with the complexity I think you're talking about.
Thanks
-- Qais Yousef
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