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Message-ID: <20110120163443.762c2409@annuminas.surriel.com>
Date: Thu, 20 Jan 2011 16:34:43 -0500
From: Rik van Riel <riel@...hat.com>
To: kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Avi Kiviti <avi@...hat.com>,
Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Mike Galbraith <efault@....de>,
Chris Wright <chrisw@...s-sol.org>, ttracy@...hat.com,
dshaks@...hat.com, "Nakajima, Jun" <jun.nakajima@...el.com>
Subject: [RFC -v6 PATCH 4/8] sched: Add yield_to(task, preempt)
functionality
From: Mike Galbraith <efault@....de>
Currently only implemented for fair class tasks.
Add a yield_to_task method() to the fair scheduling class. allowing the
caller of yield_to() to accelerate another thread in it's thread group,
task group.
Implemented via a scheduler hint, using cfs_rq->next to encourage the
target being selected. We can rely on pick_next_entity to keep things
fair, so noone can accelerate a thread that has already used its fair
share of CPU time.
This also means callers should only call yield_to when they really
mean it. Calling it too often can result in the scheduler just
ignoring the hint.
Signed-off-by: Rik van Riel <riel@...hat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
Signed-off-by: Mike Galbraith <efault@....de>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2c79e92..6c43fc4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1047,6 +1047,7 @@ struct sched_class {
void (*enqueue_task) (struct rq *rq, struct task_struct *p, int flags);
void (*dequeue_task) (struct rq *rq, struct task_struct *p, int flags);
void (*yield_task) (struct rq *rq);
+ bool (*yield_to_task) (struct rq *rq, struct task_struct *p, bool preempt);
void (*check_preempt_curr) (struct rq *rq, struct task_struct *p, int flags);
@@ -1943,6 +1944,7 @@ static inline int rt_mutex_getprio(struct task_struct *p)
# define rt_mutex_adjust_pi(p) do { } while (0)
#endif
+extern bool yield_to(struct task_struct *p, bool 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 e4e57ff..1f38ed2 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5270,6 +5270,64 @@ 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.
+ *
+ * Returns true if we indeed boosted the target task.
+ */
+bool __sched yield_to(struct task_struct *p, bool preempt)
+{
+ struct task_struct *curr = current;
+ struct rq *rq, *p_rq;
+ unsigned long flags;
+ bool yielded = 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 (!curr->sched_class->yield_to_task)
+ goto out;
+
+ if (curr->sched_class != p->sched_class)
+ goto out;
+
+ if (task_running(p_rq, p) || p->state)
+ goto out;
+
+ if (!same_thread_group(p, curr))
+ goto out;
+
+#ifdef CONFIG_FAIR_GROUP_SCHED
+ if (task_group(p) != task_group(curr))
+ goto out;
+#endif
+
+ yielded = curr->sched_class->yield_to_task(rq, p, preempt);
+
+out:
+ double_rq_unlock(rq, p_rq);
+ local_irq_restore(flags);
+
+ if (yielded)
+ yield();
+
+ return yielded;
+}
+EXPORT_SYMBOL_GPL(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 f701a51..097e936 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1800,6 +1800,23 @@ static void yield_task_fair(struct rq *rq)
set_yield_buddy(se);
}
+static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preempt)
+{
+ struct sched_entity *se = &p->se;
+
+ if (!se->on_rq)
+ return false;
+
+ /* Tell the scheduler that we'd really like pse to run next. */
+ set_next_buddy(se);
+
+ /* Make p's CPU reschedule; pick_next_entity takes care of fairness. */
+ if (preempt)
+ resched_task(rq->curr);
+
+ return true;
+}
+
#ifdef CONFIG_SMP
/**************************************************
* Fair scheduling class load-balancing methods:
@@ -3993,6 +4010,7 @@ 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,
--
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