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Date: Wed, 21 Dec 2011 01:09:44 +0400 From: Tkhai Kirill <tkhai@...dex.ru> To: Oleg Nesterov <oleg@...hat.com> Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>, Gregory Haskins <ghaskins@...ell.com> Subject: Re: [PATCH]sched_rt.c: Avoid unnecessary dequeue and enqueue of pushable tasks in set_cpus_allowed_rt() Again, right patch 21.12.2011, 00:28, "Tkhai Kirill" <tkhai@...dex.ru>: > 20.12.2011, 21:44, "Oleg Nesterov" <oleg@...hat.com>: > >> On 12/02, Kirill Tkhai wrote: >>> Migration status depends on a difference of weight from 0 and 1. If >>> weight > 1 (<= 1) and old weight <= 1 (> 1) then task becomes pushable >>> (not pushable). We are not insterested in exact values of it, is it 3 or >>> 4, for example. >>> >>> Now if we are changing affinity from a set of 3 cpus to a set of 4, the >>> task will be dequeued and enqueued sequentially without important >>> difference in comparison with initial state. The only difference is in >>> internal representation of plist queue of pushable tasks and the fact >>> that the task may won't be the first in a sequence of the same priority >>> tasks. But it seems to me it gives nothing. >> Looks reasonable, although I can't say I really understand this code. >> Add Gregory. >>> Signed-off-by: Tkhai Kirill <tkhai@...dex.ru> >>> >>> --- kernel/sched_rt.c.orig 2011-12-02 00:29:11.970243145 +0400 >>> +++ kernel/sched_rt.c 2011-12-02 00:37:43.622846606 +0400 >> please use -p1 > > Sorry, this time I'm sending "git diffed" output. > >>> @@ -1572,43 +1572,37 @@ static void set_cpus_allowed_rt(struct t >>> const struct cpumask *new_mask) >>> { >>> int weight = cpumask_weight(new_mask); >>> + struct rq *rq; >>> >>> BUG_ON(!rt_task(p)); >>> >>> /* >>> - * Update the migration status of the RQ if we have an RT task >>> - * which is running AND changing its weight value. >>> + * Just exit if it's not necessary to change migration status >>> */ >>> - if (p->on_rq && (weight != p->rt.nr_cpus_allowed)) { >>> - struct rq *rq = task_rq(p); >>> + if ((p->rt.nr_cpus_allowed <= 1 && weight <= 1) >>> + || (p->rt.nr_cpus_allowed > 1 && weight > 1)) >>> + return; >> Subjective, but may be >> >> if ((p->rt.nr_cpus_allowed > 1) != (weight > 1)) >> return; >> >> looks more understandable? > > Yes, thanks. > > --- > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index 3640ebb..4467f4d 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1774,43 +1774,36 @@ static void set_cpus_allowed_rt(struct task_struct *p, > const struct cpumask *new_mask) > { > int weight = cpumask_weight(new_mask); > + struct rq *rq; > > BUG_ON(!rt_task(p)); > > /* > - * Update the migration status of the RQ if we have an RT task > - * which is running AND changing its weight value. > + * Just exit if it's not necessary to change migration status > */ > - if (p->on_rq && (weight != p->rt.nr_cpus_allowed)) { > - struct rq *rq = task_rq(p); > - > - if (!task_current(rq, p)) { > - /* > - * Make sure we dequeue this task from the pushable list > - * before going further. It will either remain off of > - * the list because we are no longer pushable, or it > - * will be requeued. > - */ > - if (p->rt.nr_cpus_allowed > 1) > - dequeue_pushable_task(rq, p); > - > - /* > - * Requeue if our weight is changing and still > 1 > - */ > - if (weight > 1) > - enqueue_pushable_task(rq, p); > + if ((p->rt.nr_cpus_allowed > 1) != (weight > 1)) > + return; > > - } > + if (!p->on_rq) > + return; > > - if ((p->rt.nr_cpus_allowed <= 1) && (weight > 1)) { > - rq->rt.rt_nr_migratory++; > - } else if ((p->rt.nr_cpus_allowed > 1) && (weight <= 1)) { > - BUG_ON(!rq->rt.rt_nr_migratory); > - rq->rt.rt_nr_migratory--; > - } > + rq = task_rq(p); > > - update_rt_migration(&rq->rt); > + /* > + * Several cpus were allowed but now it's not so OR vice versa > + */ > + if (weight <= 1) { > + if (!task_current(rq, p)) > + dequeue_pushable_task(rq, p); > + BUG_ON(!rq->rt.rt_nr_migratory); > + rq->rt.rt_nr_migratory--; > + } else { > + if (!task_current(rq, p)) > + enqueue_pushable_task(rq, p); > + rq->rt.rt_nr_migratory++; > } > + > + update_rt_migration(&rq->rt); > } > > /* Assumes rq->lock is held */ --- diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 3640ebb..bf48343 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1774,43 +1774,36 @@ static void set_cpus_allowed_rt(struct task_struct *p, const struct cpumask *new_mask) { int weight = cpumask_weight(new_mask); + struct rq *rq; BUG_ON(!rt_task(p)); /* - * Update the migration status of the RQ if we have an RT task - * which is running AND changing its weight value. + * Just exit if it's not necessary to change migration status */ - if (p->on_rq && (weight != p->rt.nr_cpus_allowed)) { - struct rq *rq = task_rq(p); - - if (!task_current(rq, p)) { - /* - * Make sure we dequeue this task from the pushable list - * before going further. It will either remain off of - * the list because we are no longer pushable, or it - * will be requeued. - */ - if (p->rt.nr_cpus_allowed > 1) - dequeue_pushable_task(rq, p); - - /* - * Requeue if our weight is changing and still > 1 - */ - if (weight > 1) - enqueue_pushable_task(rq, p); + if ((p->rt.nr_cpus_allowed > 1) == (weight > 1)) + return; - } + if (!p->on_rq) + return; - if ((p->rt.nr_cpus_allowed <= 1) && (weight > 1)) { - rq->rt.rt_nr_migratory++; - } else if ((p->rt.nr_cpus_allowed > 1) && (weight <= 1)) { - BUG_ON(!rq->rt.rt_nr_migratory); - rq->rt.rt_nr_migratory--; - } + rq = task_rq(p); - update_rt_migration(&rq->rt); + /* + * Several cpus were allowed but now it's not so OR vice versa + */ + if (weight <= 1) { + if (!task_current(rq, p)) + dequeue_pushable_task(rq, p); + BUG_ON(!rq->rt.rt_nr_migratory); + rq->rt.rt_nr_migratory--; + } else { + if (!task_current(rq, p)) + enqueue_pushable_task(rq, p); + rq->rt.rt_nr_migratory++; } + + update_rt_migration(&rq->rt); } /* Assumes rq->lock is held */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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