linux-kernel - [PATCH 1/4] sched/fair: make sure to try to detach at least one movable task

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]

Date:   Thu, 25 Aug 2022 14:27:23 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     zhangqiao22@...wei.com,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 1/4] sched/fair: make sure to try to detach at least one movable task

During load balance, we try at most env->loop_max time to move a task.
But it can happen that the loop_max LRU tasks (ie tail of
the cfs_tasks list) can't be moved to dst_cpu because of affinity.
In this case, loop in the list until we found at least one.

The maximum of detached tasks remained the same as before.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index da388657d5ac..02b7b808e186 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8052,8 +8052,12 @@ static int detach_tasks(struct lb_env *env)
 		p = list_last_entry(tasks, struct task_struct, se.group_node);
 
 		env->loop++;
-		/* We've more or less seen every task there is, call it quits */
-		if (env->loop > env->loop_max)
+		/*
+		 * We've more or less seen every task there is, call it quits
+		 * unless we haven't found any movable task yet.
+		 */
+		if (env->loop > env->loop_max &&
+		    !(env->flags & LBF_ALL_PINNED))
 			break;
 
 		/* take a breather every nr_migrate tasks */
@@ -10182,7 +10186,9 @@ static int load_balance(int this_cpu, struct rq *this_rq,
 
 		if (env.flags & LBF_NEED_BREAK) {
 			env.flags &= ~LBF_NEED_BREAK;
-			goto more_balance;
+			/* Stop if we tried all running tasks */
+			if (env.loop < busiest->nr_running)
+				goto more_balance;
 		}
 
 		/*
-- 
2.17.1