linux-kernel - [PATCH] sched_rt: don't allocate cpumask in fastpath

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Message-Id: <200903251501.22664.rusty@rustcorp.com.au>
Date:	Wed, 25 Mar 2009 15:01:22 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] sched_rt: don't allocate cpumask in fastpath

Impact: cleanup

As pointed out by Steven Rostedt.  Since the arg in question is
unused, we simply change cpupri_find() to accept NULL.

Cc: Steven Rostedt <srostedt@...hat.com>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
---
 kernel/sched_cpupri.c |    5 +++--
 kernel/sched_rt.c     |   15 ++++-----------
 2 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/kernel/sched_cpupri.c b/kernel/sched_cpupri.c
--- a/kernel/sched_cpupri.c
+++ b/kernel/sched_cpupri.c
@@ -55,7 +55,7 @@ static int convert_prio(int prio)
  * cpupri_find - find the best (lowest-pri) CPU in the system
  * @cp: The cpupri context
  * @p: The task
- * @lowest_mask: A mask to fill in with selected CPUs
+ * @lowest_mask: A mask to fill in with selected CPUs (or NULL)
  *
  * Note: This function returns the recommended CPUs as calculated during the
  * current invokation.  By the time the call returns, the CPUs may have in
@@ -81,7 +81,8 @@ int cpupri_find(struct cpupri *cp, struc
 		if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
 			continue;
 
-		cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
+		if (lowest_mask)
+			cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
 		return 1;
 	}
 
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -805,20 +805,15 @@ static int select_task_rq_rt(struct task
 
 static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
 {
-	cpumask_var_t mask;
-
 	if (rq->curr->rt.nr_cpus_allowed == 1)
 		return;
 
-	if (!alloc_cpumask_var(&mask, GFP_ATOMIC))
+	if (p->rt.nr_cpus_allowed != 1
+	    && cpupri_find(&rq->rd->cpupri, p, NULL))
 		return;
 
-	if (p->rt.nr_cpus_allowed != 1
-	    && cpupri_find(&rq->rd->cpupri, p, mask))
-		goto free;
-
-	if (!cpupri_find(&rq->rd->cpupri, rq->curr, mask))
-		goto free;
+	if (!cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
+		return;
 
 	/*
 	 * There appears to be other cpus that can accept
@@ -827,8 +822,6 @@ static void check_preempt_equal_prio(str
 	 */
 	requeue_task_rt(rq, p, 1);
 	resched_task(rq->curr);
-free:
-	free_cpumask_var(mask);
 }
 
 #endif /* CONFIG_SMP */
--
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