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From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Rik van Riel <riel@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Avi Kiviti <avi@redhat.com>,
	Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
	Mike Galbraith <efault@gmx.de>,
	Chris Wright <chrisw@sous-sol.org>,
	"Nakajima, Jun" <jun.nakajima@intel.com>
Subject: Re: [PATCH -v8a 4/7] sched: Add yield_to(task, preempt) functionality
Date: Tue, 01 Feb 2011 16:52:02 +0100	[thread overview]
Message-ID: <1296575522.26581.210.camel@laptop> (raw)
In-Reply-To: <20110201095051.4ddb7738@annuminas.surriel.com>

On Tue, 2011-02-01 at 09:50 -0500, Rik van Riel wrote:

> +/**
> + * 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;
> +
> +	yielded = curr->sched_class->yield_to_task(rq, p, preempt);
> +
> +	if (yielded) {
> +		schedstat_inc(rq, yld_count);
> +		current->sched_class->yield_task(rq);
> +	}

We can avoid this second indirect function call by

> +
> +out:
> +	double_rq_unlock(rq, p_rq);
> +	local_irq_restore(flags);
> +
> +	if (yielded)
> +		schedule();
> +
> +	return yielded;
> +}
> +EXPORT_SYMBOL_GPL(yield_to);


> +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);

calling: yield_task_fair(rq); here.

> +	return true;
> +}


I'll make that change on commit.

  reply	other threads:[~2011-02-01 15:51 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-02-01 14:44 [PATCH -v8a 0/7] directed yield for Pause Loop Exiting Rik van Riel
2011-02-01 14:47 ` [PATCH -v8a 1/7] sched: check the right ->nr_running in yield_task_fair Rik van Riel
2011-02-03 14:11   ` [tip:sched/core] sched: Check the right ->nr_running in yield_task_fair() tip-bot for Rik van Riel
2011-02-01 14:48 ` [PATCH -v8a 2/7] sched: limit the scope of clear_buddies Rik van Riel
2011-02-03 14:11   ` [tip:sched/core] sched: Limit " tip-bot for Rik van Riel
2011-02-01 14:50 ` [PATCH -v8a 4/7] sched: Add yield_to(task, preempt) functionality Rik van Riel
2011-02-01 15:52   ` Peter Zijlstra [this message]
2011-02-03 12:58   ` Peter Zijlstra
2011-02-03 14:12   ` [tip:sched/core] " tip-bot for Mike Galbraith
2011-02-26  0:43     ` Venkatesh Pallipadi
2011-02-26  5:44       ` Rik van Riel
2011-02-28  9:26         ` Mike Galbraith
2011-03-02  0:28           ` [PATCH] sched: resched proper CPU on yield_to Venkatesh Pallipadi
2011-03-02  3:33             ` Rik van Riel
2011-03-02  3:37               ` Venkatesh Pallipadi
2011-03-02  3:52             ` Rik van Riel
2011-03-04 11:50             ` [tip:sched/core] sched: Resched proper CPU on yield_to() tip-bot for Venkatesh Pallipadi
2011-02-01 14:51 ` [PATCH -v8a 3/7] sched: use a buddy to implement yield_task_fair Rik van Riel
2011-02-01 15:53   ` Peter Zijlstra
2011-02-03 12:58   ` Peter Zijlstra
2011-02-03 14:12   ` [tip:sched/core] sched: Use a buddy to implement yield_task_fair() tip-bot for Rik van Riel
2011-02-01 14:51 ` [PATCH -v8a 5/7] export pid symbols needed for kvm_vcpu_on_spin Rik van Riel
2011-02-01 14:52 ` [PATCH -v8a 6/7] kvm: keep track of which task is running a KVM vcpu Rik van Riel
2011-02-01 14:53 ` [PATCH -v8a 7/7] kvm: use yield_to instead of sleep in kvm_vcpu_on_spin Rik van Riel
2011-02-07  9:08 ` [PATCH -v8a 0/7] directed yield for Pause Loop Exiting Avi Kivity

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