linux-kernel - [PATCH 11/13] RT: Condense NORMAL and IDLE priorities

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Date:	Tue, 23 Oct 2007 12:51:19 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	linux-rt-users@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Gregory Haskins <ghaskins@...ell.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Darren Hart <dvhltc@...ibm.com>
Subject: [PATCH 11/13] RT: Condense NORMAL and IDLE priorities

We only need to track if the CPU is in a non-RT state, as opposed to its
priority within the non-RT state.  So simplify setting in the effort of
reducing cache-thrash.

Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
---

 kernel/sched.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index a1f1d92..4abe738 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -371,11 +371,19 @@ static inline void set_rq_prio(struct rq *rq, int prio)
 	rq->highest_prio = prio;
 }
 
+/*
+ * We dont care what the exact normal priority is.  We only care about
+ * RT-priority, vs non-RT (normal or idle).  So flatten the priority if its a
+ * non-RT variety. This will reduce cache-thrashing on the rq->highest_prio.
+ */
 static inline void update_rq_prio(struct rq *rq)
 {
 	struct rt_prio_array *array = &rq->rt.active;
 	int                   prio  = sched_find_first_bit(array->bitmap);
 
+	if ((prio != MAX_PRIO) && (prio > MAX_RT_PRIO))
+		prio = MAX_RT_PRIO;
+
 	if (rq->highest_prio != prio)
 		set_rq_prio(rq, prio);
 }

-
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