linux-kernel - [PATCH 32/33] sched: Add hysteresis to p->numa

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Date:	Thu, 22 Nov 2012 23:49:53 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Turner <pjt@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>
Subject: [PATCH 32/33] sched: Add hysteresis to p->numa_shared

Make p->numa_shared flip/flop less around unstable equilibriums,
instead require a significant move in either direction to trigger
'dominantly shared accesses' versus 'dominantly private accesses'
NUMA status.

Suggested-by: Rik van Riel <riel@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8aa4b36..ab4a7130 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1111,7 +1111,20 @@ static void task_numa_placement(struct task_struct *p)
 	 * we might want to consider a different equation below to reduce
 	 * the impact of a little private memory accesses.
 	 */
-	shared = (total[0] >= total[1] / 2);
+	shared = p->numa_shared;
+
+	if (shared < 0) {
+		shared = (total[0] >= total[1]);
+	} else if (shared == 0) {
+		/* If it was private before, make it harder to become shared: */
+		if (total[0] >= total[1]*2)
+			shared = 1;
+	} else if (shared == 1 ) {
+		 /* If it was shared before, make it harder to become private: */
+		if (total[0]*2 <= total[1])
+			shared = 0;
+	}
+
 	if (shared)
 		p->ideal_cpu = sched_update_ideal_cpu_shared(p);
 	else
-- 
1.7.11.7

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