linux-kernel - [PATCH 6/6] numa,sched: do statistics calculation using local variables only

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1390245667-24193-7-git-send-email-riel@redhat.com>
Date:	Mon, 20 Jan 2014 14:21:07 -0500
From:	riel@...hat.com
To:	linux-kernel@...r.kernel.org
Cc:	linux-mm@...ck.org, peterz@...radead.org, mgorman@...e.de,
	mingo@...hat.com, chegu_vinod@...com
Subject: [PATCH 6/6] numa,sched: do statistics calculation using local variables only

From: Rik van Riel <riel@...hat.com>

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.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Chegu Vinod <chegu_vinod@...com>
Signed-off-by: Rik van Riel <riel@...hat.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 203877d..ad30d14 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1456,12 +1456,9 @@ 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[i];
-			f_diff = -p->numa_faults_from[i];
 
 			/* Decay existing window, copy faults since last scan */
-			p->numa_faults[i] >>= 1;
-			p->numa_faults[i] += p->numa_faults_buffer[i];
+			diff = p->numa_faults_buffer[i] - p->numa_faults[i] / 2;
 			fault_types[priv] += p->numa_faults_buffer[i];
 			p->numa_faults_buffer[i] = 0;
 
@@ -1475,13 +1472,12 @@ static void task_numa_placement(struct task_struct *p)
 			f_weight = (16384 * runtime *
 				   p->numa_faults_from_buffer[i]) /
 				   (total_faults * period + 1);
-			p->numa_faults_from[i] >>= 1;
-			p->numa_faults_from[i] += f_weight;
+			f_diff = f_weight - p->numa_faults_from[i] / 2;
 			p->numa_faults_from_buffer[i] = 0;
 
+			p->numa_faults[i] += diff;
+			p->numa_faults_from[i] += f_diff;
 			faults += p->numa_faults[i];
-			diff += p->numa_faults[i];
-			f_diff += p->numa_faults_from[i];
 			p->total_numa_faults += diff;
 			if (p->numa_group) {
 				/* safe because we can only change our own group */
-- 
1.8.4.2

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/