linux-kernel - [PATCH 1/2] sched: Optimise task_mm_cid

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: <20241202140735.56368-2-gmonaco@redhat.com>
Date: Mon,  2 Dec 2024 15:07:34 +0100
From: Gabriele Monaco <gmonaco@...hat.com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Cc: Gabriele Monaco <gmonaco@...hat.com>
Subject: [PATCH 1/2] sched: Optimise task_mm_cid_work duration

The current behaviour of task_mm_cid_work is to loop through all
possible CPUs twice to clean up old mm_cid remotely, this can be a waste
of resources especially on tasks with a CPU affinity.

This patch reduces the CPUs involved in the remote CID cleanup carried
on by task_mm_cid_work.

Using the mm_cidmask for the remote cleanup can considerably reduce the
function runtime in highly isolated environments, where each process has
affinity to a single core.  Likewise, in the worst case, the mask is
equivalent to all possible CPUs and we don't see any difference with the
current behaviour.

Signed-off-by: Gabriele Monaco <gmonaco@...hat.com>
---
 kernel/sched/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 95e40895a519..57b50b5952fa 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10553,14 +10553,14 @@ static void task_mm_cid_work(struct callback_head *work)
 		return;
 	cidmask = mm_cidmask(mm);
 	/* Clear cids that were not recently used. */
-	for_each_possible_cpu(cpu)
+	for_each_cpu_from(cpu, cidmask)
 		sched_mm_cid_remote_clear_old(mm, cpu);
 	weight = cpumask_weight(cidmask);
 	/*
 	 * Clear cids that are greater or equal to the cidmask weight to
 	 * recompact it.
 	 */
-	for_each_possible_cpu(cpu)
+	for_each_cpu_from(cpu, cidmask)
 		sched_mm_cid_remote_clear_weight(mm, cpu, weight);
 }
 
-- 
2.47.0