From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lukasz Majewski Subject: [PATCH 2/2] sched:fix: Signed overflow prevention for vacancy calculation Date: Thu, 23 May 2013 10:34:24 +0200 Message-ID: <1369298064-14998-2-git-send-email-l.majewski@samsung.com> References: <1369298064-14998-1-git-send-email-l.majewski@samsung.com> Return-path: In-reply-to: <1369298064-14998-1-git-send-email-l.majewski@samsung.com> Sender: linux-kernel-owner@vger.kernel.org To: Alex Shi Cc: Linux PM list , Vincent Guittot , Lukasz Majewski , Jonghwa Lee , Myungjoo Ham , linux-kernel , Kyungmin Park List-Id: linux-pm@vger.kernel.org Nasty bug with vacancy calculation has been fixed. In the if statement the FULL_UTIL is a large constant, max_cfs_util() returns unsigned and putil is also defined as unsigned. The outcome is that this condition is always true. As observed, this was the reason for frequent jumps of processes between CPUs. Signed-off-by: Lukasz Majewski Signed-off-by: Kyungmin Park --- This patch was developed on top of the following Alex's repository: https://github.com/alexshi/power-scheduling/commits/power-scheduling --- kernel/sched/fair.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 14d29b3..8b07f6c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3476,9 +3476,10 @@ find_leader_cpu(struct sched_group *group, struct task_struct *p, int this_cpu, do_div(tmp, (p->se.avg.runnable_avg_period + 1)); putil = (unsigned) tmp; + vacancy = (int) (FULL_UTIL - max_cfs_util(this_cpu, wakeup) - + (putil << 2)); /* bias toward local cpu */ - if (cpumask_test_cpu(this_cpu, tsk_cpus_allowed(p)) && - FULL_UTIL - max_cfs_util(this_cpu, wakeup) - (putil << 2) > 0) + if (cpumask_test_cpu(this_cpu, tsk_cpus_allowed(p)) && vacancy > 0) return this_cpu; /* Traverse only the allowed CPUs */ -- 1.7.10.4