linux-kernel - [PATCH 2/2] sched/fair: Improve the for loop in select_idle

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: <6b165676325a47d67e667582a7b78da85c5c118a.1549536337.git.viresh.kumar@linaro.org>
Date:   Thu,  7 Feb 2019 16:16:06 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] sched/fair: Improve the for loop in select_idle_core()

Once a non-idle thread is found for a core, there is no point in
traversing rest of the threads of that core. We continue traversal
currently to clear those threads from "cpus" mask. Clear all the
threads with a single call to cpumask_andnot(), which will also let us
exit the loop earlier.

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 kernel/sched/fair.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8d5c82342a36..ccd0ae9878a2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6068,6 +6068,7 @@ void __update_idle_core(struct rq *rq)
 static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
 {
 	struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
+	const struct cpumask *smt;
 	int core, cpu;
 
 	if (!static_branch_likely(&sched_smt_present))
@@ -6081,10 +6082,14 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
 	for_each_cpu_wrap(core, cpus, target) {
 		bool idle = true;
 
-		for_each_cpu(cpu, cpu_smt_mask(core)) {
-			cpumask_clear_cpu(cpu, cpus);
-			if (!available_idle_cpu(cpu))
+		smt = cpu_smt_mask(core);
+		cpumask_andnot(cpus, cpus, smt);
+
+		for_each_cpu(cpu, smt) {
+			if (!available_idle_cpu(cpu)) {
 				idle = false;
+				break;
+			}
 		}
 
 		if (idle)
-- 
2.20.1.321.g9e740568ce00