linux-kernel - Re:[PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

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Date:	Tue, 29 Jan 2013 18:45:07 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re:[PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

> On Tue, 2013-01-29 at 00:23 +0400, Kirill Tkhai wrote:
> 
>> Just switched pinned task is not able to be pushed. If the rq had had
>> several RT tasks before they have already been considered as candidates
>> to be pushed (or pulled).
> 
> Thanks, but I have one minor nit.
> 
>> Signed-off-by: Kirill V Tkhai <tkhai@...dex.ru>
>> CC: Steven Rostedt <rostedt@...dmis.org>
>> CC: Ingo Molnar <mingo@...nel.org>
>> CC: Peter Zijlstra <peterz@...radead.org>
>> CC: linux-rt-users <linux-rt-users@...r.kernel.org>
>> ---
>> kernel/sched/rt.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>> index 4e8f0f4..5f7d92b 100644
>> --- a/kernel/sched/rt.c
>> +++ b/kernel/sched/rt.c
>> @@ -1925,9 +1925,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
>> */
>> if (p->on_rq && rq->curr != p) {
>> #ifdef CONFIG_SMP
>> - if (rq->rt.overloaded && push_rt_task(rq) &&
>> + if (rq->rt.overloaded && p->nr_cpus_allowed > 1 &&
> 
> I would swap the order here. That is, check p->nr_cpus_allowed before
> rq->rt.overloaded. The order doesn't really matter, and even though
> rq->rt.overloaded is probably more likely to be 0, it is used by other
> CPUs. And as a micro-optimization, I rather read something that is used
> by only one CPU than to read something that may be modified by many
> CPUs.
> 
> -- Steve
> 

I corrected. Thanks.

[PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

Just switched pinned task is not able to be pushed. If the rq had had
several RT tasks before they have already been considered as candidates
to be pushed (or pulled).

Signed-off-by: Kirill V Tkhai <tkhai@...dex.ru>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Ingo Molnar <mingo@...nel.org>
CC: Peter Zijlstra <peterz@...radead.org>
CC: linux-rt-users <linux-rt-users@...r.kernel.org>
---
 kernel/sched/rt.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4e8f0f4..5aab032 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1925,9 +1925,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
 	 */
 	if (p->on_rq && rq->curr != p) {
 #ifdef CONFIG_SMP
-		if (rq->rt.overloaded && push_rt_task(rq) &&
+		if (p->nr_cpus_allowed > 1 && rq->rt.overloaded &&
 		    /* Don't resched if we changed runqueues */
-		    rq != task_rq(p))
+		    push_rt_task(rq) && rq != task_rq(p))
 			check_resched = 0;
 #endif /* CONFIG_SMP */
 		if (check_resched && p->prio < rq->curr->prio)
--
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