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Tue, 20 Oct 2026 11:54:13 -0700 (PDT) Received: from lima-kdev.local ([85.100.66.184]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a1fb845dc2sm15895005e9.8.2026.10.20.11.54.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Oct 2026 11:54:13 -0700 (PDT) From: Kayra Cizmeci To: peterz@infradead.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Ricardo Neri , Chen Yu , Tim Chen Cc: linux-kernel@vger.kernel.org, Kayra Cizmeci Subject: [PATCH v2] sched/cache: Ignore non-fair current in alb_break_llc() Date: Tue, 20 Oct 2026 21:54:01 +0300 Message-ID: <20261020185402.57017-1-kayracizmeci@gmail.com> X-Mailer: git-send-email 2.53.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Commit d6b9afab44e23 ("sched/cache: Fix checking active load balance by only considering the CFS task") stopped using task_util() for non-fair cur. __active_load_balance_cpu_stop() calls detach_one_task(), that only looks to cfs_tasks list. So if the rq->curr is not fair, doing a decision according to it is wrong, since we only migrate tasks that is fair. Commit f0d243a96f26 ("sched/fair: Avoid creating misfits during cache-aware balancing") passes cur to task_misfits_asym_cpu() without checking if the cur is in fair class or not. Fix this. Fixes: f0d243a96f26 ("sched/fair: Avoid creating misfits during cache-aware balancing") Signed-off-by: Kayra Cizmeci --- Changes v1->v2: * Add suggested comment (Tim Chen :>) * Change the changelog so that it says the issue is passing a non-fair cur to task_misfits_asym_cpu() This versions not compile-tested. Tho only change is this comment, so it should be fine. Right? ;-). kernel/sched/fair.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0feec172fd37..9d7fd6cec376 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -11016,7 +11016,14 @@ alb_break_llc(struct lb_env *env) return true; cur = rcu_dereference_all(env->src_rq->curr); - if (cur && cur->sched_class == &fair_sched_class) + /* + * Active balance only detaches CFS tasks, so a non-fair + * curr is never migrated. Ignore it and avoid using its + * stale util in the misfit and LLC checks. + */ + if (cur && cur->sched_class != &fair_sched_class) + cur = NULL; + if (cur) util = task_util(cur); if (task_misfits_asym_cpu(env, cur) || -- 2.53.0