From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756482AbbKEU4e (ORCPT ); Thu, 5 Nov 2015 15:56:34 -0500 Received: from shelob.surriel.com ([74.92.59.67]:60044 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755198AbbKEU43 (ORCPT ); Thu, 5 Nov 2015 15:56:29 -0500 From: riel@redhat.com To: linux-kernel@vger.kernel.org Cc: peterz@infradead.org, mingo@kernel.org, jstancek@redhat.com, mgorman@suse.de Subject: [PATCH 1/2] sched,numa: fix math underflow in task_tick_numa Date: Thu, 5 Nov 2015 15:56:22 -0500 Message-Id: <1446756983-28173-2-git-send-email-riel@redhat.com> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1446756983-28173-1-git-send-email-riel@redhat.com> References: <1446756983-28173-1-git-send-email-riel@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Rik van Riel The NUMA balancing code implements delays in scanning by advancing curr->node_stamp beyond curr->se.sum_exec_runtime. With unsigned math, that creates an underflow, which results in task_numa_work being queued all the time, even when we don't want to. Avoiding the math underflow makes it possible to reduce CPU overhead in the NUMA balancing code. Signed-off-by: Rik van Riel Reported-and-tested-by: Jan Stancek --- 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 824aa9f501a3..f04fda8f669c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2302,7 +2302,7 @@ void task_tick_numa(struct rq *rq, struct task_struct *curr) now = curr->se.sum_exec_runtime; period = (u64)curr->numa_scan_period * NSEC_PER_MSEC; - if (now - curr->node_stamp > period) { + if (now > curr->node_stamp + period) { if (!curr->node_stamp) curr->numa_scan_period = task_scan_min(curr); curr->node_stamp += period; -- 2.1.0