Messages in this thread | | | Date | Tue, 4 Jan 2011 22:28:16 +0800 | Subject | Re: [RFC -v3 PATCH 2/3] sched: add yield_to function | From | Hillf Danton <> |
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On Tue, Jan 4, 2011 at 5:29 AM, Rik van Riel <riel@redhat.com> wrote: > From: Mike Galbraith <efault@gmx.de> > > Add a yield_to function to the scheduler code, allowing us to > give enough of our timeslice to another thread to allow it to > run and release whatever resource we need it to release. > > We may want to use this to provide a sys_yield_to system call > one day. > > Signed-off-by: Rik van Riel <riel@redhat.com> > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> > Not-signed-off-by: Mike Galbraith <efault@gmx.de> > > --- > Mike, want to change the above into a Signed-off-by: ? :) > This code seems to work well. > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index c5f926c..0b8a3e6 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1083,6 +1083,7 @@ struct sched_class { > void (*enqueue_task) (struct rq *rq, struct task_struct *p, int wakeup); > void (*dequeue_task) (struct rq *rq, struct task_struct *p, int sleep); > void (*yield_task) (struct rq *rq); > + int (*yield_to_task) (struct task_struct *p, int preempt); > > void (*check_preempt_curr) (struct rq *rq, struct task_struct *p, int flags); > > @@ -1981,6 +1982,7 @@ static inline int rt_mutex_getprio(struct task_struct *p) > # define rt_mutex_adjust_pi(p) do { } while (0) > #endif > > +extern void yield_to(struct task_struct *p, int preempt); > extern void set_user_nice(struct task_struct *p, long nice); > extern int task_prio(const struct task_struct *p); > extern int task_nice(const struct task_struct *p); > diff --git a/kernel/sched.c b/kernel/sched.c > index f8e5a25..ffa7a9d 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -6901,6 +6901,53 @@ void __sched yield(void) > } > EXPORT_SYMBOL(yield); > > +/** > + * yield_to - yield the current processor to another thread in > + * your thread group, or accelerate that thread toward the > + * processor it's on. > + * > + * It's the caller's job to ensure that the target task struct > + * can't go away on us before we can do any checks. > + */ > +void __sched yield_to(struct task_struct *p, int preempt) > +{ > + struct task_struct *curr = current; > + struct rq *rq, *p_rq; > + unsigned long flags; > + int yield = 0; > + > + local_irq_save(flags); > + rq = this_rq(); > + > +again: > + p_rq = task_rq(p); > + double_rq_lock(rq, p_rq); > + while (task_rq(p) != p_rq) { > + double_rq_unlock(rq, p_rq); > + goto again; > + } > + > + if (task_running(p_rq, p) || p->state || !p->se.on_rq || > + !same_thread_group(p, curr) || > + !curr->sched_class->yield_to_task || > + curr->sched_class != p->sched_class) { > + goto out; > + } > + > + yield = curr->sched_class->yield_to_task(p, preempt); > + > +out: > + double_rq_unlock(rq, p_rq); > + local_irq_restore(flags); > + > + if (yield) { > + set_current_state(TASK_RUNNING); > + schedule(); > + } > +} > +EXPORT_SYMBOL(yield_to); > + > + > /* > * This task is about to go to sleep on IO. Increment rq->nr_iowait so > * that process accounting knows that this is a task in IO wait state. > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c > index 5119b08..3288e7c 100644 > --- a/kernel/sched_fair.c > +++ b/kernel/sched_fair.c > @@ -1119,6 +1119,61 @@ static void yield_task_fair(struct rq *rq) > } > > #ifdef CONFIG_SMP > +static void pull_task(struct rq *src_rq, struct task_struct *p, > + struct rq *this_rq, int this_cpu); > +#endif > + > +static int yield_to_task_fair(struct task_struct *p, int preempt) > +{ > + struct sched_entity *se = ¤t->se; > + struct sched_entity *pse = &p->se; > + struct sched_entity *curr = &(task_rq(p)->curr)->se; > + struct cfs_rq *cfs_rq = cfs_rq_of(se); > + struct cfs_rq *p_cfs_rq = cfs_rq_of(pse); > + int yield = this_rq() == task_rq(p); > + int want_preempt = preempt; > + > +#ifdef CONFIG_FAIR_GROUP_SCHED > + if (cfs_rq->tg != p_cfs_rq->tg) > + return 0; > + > + /* Preemption only allowed within the same task group. */ > + if (preempt && cfs_rq->tg != cfs_rq_of(curr)->tg) > + preempt = 0; > +#endif > + /* Preemption only allowed within the same thread group. */ > + if (preempt && !same_thread_group(current, task_of(p_cfs_rq->curr))) > + preempt = 0; > + > +#ifdef CONFIG_SMP > + /* > + * If this yield is important enough to want to preempt instead > + * of only dropping a ->next hint, we're alone, and the target > + * is not alone, pull the target to this cpu. > + */ > + if (want_preempt && !yield && cfs_rq->nr_running == 1 && > + cpumask_test_cpu(smp_processor_id(), &p->cpus_allowed)) { > + pull_task(task_rq(p), p, this_rq(), smp_processor_id()); > + p_cfs_rq = cfs_rq_of(pse); > + yield = 1; > + } > +#endif > + > + if (yield) > + clear_buddies(cfs_rq, se); > + else if (preempt) > + clear_buddies(p_cfs_rq, curr); > + > + /* Tell the scheduler that we'd really like pse to run next. */ > + p_cfs_rq->next = pse;
If not pulled and this_rq() != task_rq(p), only assigning ->next could kick p onto its CPU?
If not, how is the lock contention eased then?
A few words to explain please.
thanks Hillf
> + > + if (!yield && preempt) > + resched_task(task_of(p_cfs_rq->curr)); > + > + return yield; > +} > + > +#ifdef CONFIG_SMP > > #ifdef CONFIG_FAIR_GROUP_SCHED > /* > @@ -2081,6 +2136,7 @@ static const struct sched_class fair_sched_class = { > .enqueue_task = enqueue_task_fair, > .dequeue_task = dequeue_task_fair, > .yield_task = yield_task_fair, > + .yield_to_task = yield_to_task_fair, > > .check_preempt_curr = check_preempt_wakeup, > > > -- > 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/ > > > -- 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/
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