linux-kernel - [patch] sched: make cpu_clock() not use the rq clock

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Message-ID: <20070726090012.GA5287@elte.hu>
Date:	Thu, 26 Jul 2007 11:00:12 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: [patch] sched: make cpu_clock() not use the rq clock

Subject: sched: make cpu_clock() not use the rq clock
From: Ingo Molnar <mingo@...e.hu>

it is enough to disable interrupts to get the precise rq-clock
of the local CPU.

this also solves an NMI watchdog regression: the NMI watchdog
calls touch_softlockup_watchdog(), which might deadlock on
rq->lock if the NMI hits an rq-locked critical section.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

Index: linux-rt-rebase.q/kernel/sched.c
===================================================================
--- linux-rt-rebase.q.orig/kernel/sched.c
+++ linux-rt-rebase.q/kernel/sched.c
@@ -446,13 +446,12 @@ static inline unsigned long long rq_cloc
  */
 unsigned long long cpu_clock(int cpu)
 {
-	struct rq *rq = cpu_rq(cpu);
 	unsigned long long now;
 	unsigned long flags;
 
-	spin_lock_irqsave(&rq->lock, flags);
-	now = rq_clock(rq);
-	spin_unlock_irqrestore(&rq->lock, flags);
+	local_irq_save(flags);
+	now = rq_clock(cpu_rq(cpu));
+	local_irq_restore(flags);
 
 	return now;
 }
-
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