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Sun, 23 Aug 2026 19:33:43 -0700 (PDT) From: Lu Wang To: Peter Zijlstra Cc: Lu Wang , mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, yu.c.chen@intel.com, tim.c.chen@linux.intel.com, chen.yu@linux.dev, kprateek.nayak@amd.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] sched/cache: honor migrate_llc_task semantics in active load balance Date: Mon, 24 Aug 2026 10:33:23 +0800 Message-ID: <20260824023324.3663800-1-wanglu.priv@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260813045241.3039862-1-wanglu.priv@gmail.com> References: <20260813045241.3039862-1-wanglu.priv@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit > CAS introduced the migrate_llc_task migration type to direct tasks > toward their preferred LLC, but its semantics can be lost when passive > load balance falls back to active load balance. This may allow ALB to > select a candidate whose preferred LLC does not match the destination, > moving it away from its preferred LLC. > > Example scenario: > > src_rq has two runnable tasks, p1 and p2. p1 prefers dst_rq (dst_llc), > while p2 prefers src_rq (src_llc). In this case, migrate_llc_task is > set because src_rq has at least one task, p1, that wants to migrate to > dst_rq. In ALB, can_migrate_task() finds p2 and returns true for it, > thus moving p2 out of its preferred LLC. > > Solution: > > The CPU stopper in ALB constructs a fresh lb_env that does not inherit > migration_type from the passive load-balance pass. Two approaches are > possible: > > (a) Add a new member to struct rq so ALB can inherit migrate_llc_task > from the passive LB that triggered it. > > (b) Define a new flag LBF_ACTIVE_LB_LLC and select the stopper callback > at kick time to preserve the migration semantics across the > asynchronous boundary. > > We choose (b) because it avoids passing migration_type through the > stopper, which would affect the meaning of migration_type for > delayed-dequeue tasks. Hi Peter, Just a gentle ping on this patch. The v3 received Reviewed-by tags from Tim Chen and Chen Yu. Would you be happy to take this patch, or are any further changes needed? Thanks, Lu