linux-kernel - [PATCH RFC] sched,numa: decay wakee

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Message-ID: <20140516001332.67f91af2@annuminas.surriel.com>
Date:	Fri, 16 May 2014 00:13:32 -0400
From:	Rik van Riel <riel@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	peterz@...radead.org, chegu_vinod@...com, mingo@...nel.org,
	umgwanakikbuti@...il.com
Subject: [PATCH RFC] sched,numa: decay wakee_flips instead of zeroing

Affine wakeups have the potential to interfere with NUMA placement.
If a task wakes up too many other tasks, affine wakeups will get
disabled.

However, regardless of how many other tasks it wakes up, it gets
re-enabled once a second, potentially interfering with NUMA
placement of other tasks.

By decaying wakee_wakes in half instead of zeroing it, we can avoid
that problem for some workloads.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4f01e2f1..0381b11 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4009,7 +4009,7 @@ static void record_wakee(struct task_struct *p)
 	 * about the loss.
 	 */
 	if (jiffies > current->wakee_flip_decay_ts + HZ) {
-		current->wakee_flips = 0;
+		current->wakee_flips >>= 1;
 		current->wakee_flip_decay_ts = jiffies;
 	}
 
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