[tip:sched/core] sched/numa: Decay -> wakee_flips instead of zeroing

[tip-bot for Rik van Riel <tipbot@zytor.com>]

Commit-ID:  096aa33863a5e48de52d2ff30e0801b7487944f4
Gitweb:     http://git.kernel.org/tip/096aa33863a5e48de52d2ff30e0801b7487944f4
Author:     Rik van Riel <riel@redhat.com>
AuthorDate: Fri, 16 May 2014 00:13:32 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 22 May 2014 11:16:41 +0200

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@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: chegu_vinod@hp.com
Cc: umgwanakikbuti@gmail.com
Link: http://lkml.kernel.org/r/20140516001332.67f91af2@annuminas.surriel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 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 503f750..c9617b7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4065,7 +4065,7 @@ 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;
 	}