[linux-yocto] [PATCH 07/28] sched/numa: Do statistics calculation using local variables only

[Yang Shi]

From: Rik van Riel <riel at redhat.com>

commit 35664fd41e1c8cc4f0b89f6a51db5af39ba50640 upstream

The current code in task_numa_placement calculates the difference
between the old and the new value, but also temporarily stores half
of the old value in the per-process variables.

The NUMA balancing code looks at those per-process variables, and
having other tasks temporarily see halved statistics could lead to
unwanted numa migrations. This can be avoided by doing all the math
in local variables.

This change also simplifies the code a little.

Signed-off-by: Rik van Riel <riel at redhat.com>
Acked-by: Mel Gorman <mgorman at suse.de>
Signed-off-by: Peter Zijlstra <peterz at infradead.org>
Cc: Chegu Vinod <chegu_vinod at hp.com>
Link: http://lkml.kernel.org/r/1390860228-21539-8-git-send-email-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Yang Shi <yang.shi at windriver.com>
---
 kernel/sched/fair.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5b9d4c9..f88b7e0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1517,12 +1517,9 @@ static void task_numa_placement(struct task_struct *p)
 			long diff, f_diff, f_weight;
 
 			i = task_faults_idx(nid, priv);
-			diff = -p->numa_faults_memory[i];
-			f_diff = -p->numa_faults_cpu[i];
 
 			/* Decay existing window, copy faults since last scan */
-			p->numa_faults_memory[i] >>= 1;
-			p->numa_faults_memory[i] += p->numa_faults_buffer_memory[i];
+			diff = p->numa_faults_buffer_memory[i] - p->numa_faults_memory[i] / 2;
 			fault_types[priv] += p->numa_faults_buffer_memory[i];
 			p->numa_faults_buffer_memory[i] = 0;
 
@@ -1536,13 +1533,12 @@ static void task_numa_placement(struct task_struct *p)
 			f_weight = div64_u64(runtime << 16, period + 1);
 			f_weight = (f_weight * p->numa_faults_buffer_cpu[i]) /
 				   (total_faults + 1);
-			p->numa_faults_cpu[i] >>= 1;
-			p->numa_faults_cpu[i] += f_weight;
+			f_diff = f_weight - p->numa_faults_cpu[i] / 2;
 			p->numa_faults_buffer_cpu[i] = 0;
 
+			p->numa_faults_memory[i] += diff;
+			p->numa_faults_cpu[i] += f_diff;
 			faults += p->numa_faults_memory[i];
-			diff += p->numa_faults_memory[i];
-			f_diff += p->numa_faults_cpu[i];
 			p->total_numa_faults += diff;
 			if (p->numa_group) {
 				/* safe because we can only change our own group */
-- 
2.0.2