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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2025-10-28 at 23:15 +0800, Chen, Yu C wrote: > On 10/27/2025 2:04 PM, K Prateek Nayak wrote: > > Hello Tim, > >=20 > > On 10/11/2025 11:54 PM, Tim Chen wrote: > > > @@ -3999,6 +4038,7 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, s= truct sched_entity *se) > > > struct rq *rq =3D rq_of(cfs_rq); > > > =20 > > > account_numa_enqueue(rq, task_of(se)); > > > + account_llc_enqueue(rq, task_of(se)); > > > list_add(&se->group_node, &rq->cfs_tasks); > > > } > > > cfs_rq->nr_queued++; > > > @@ -4010,9 +4050,14 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, = struct sched_entity *se) > > > update_load_sub(&cfs_rq->load, se->load.weight); > > > if (entity_is_task(se)) { > > > account_numa_dequeue(rq_of(cfs_rq), task_of(se)); > > > + account_llc_dequeue(rq_of(cfs_rq), task_of(se)); > > > list_del_init(&se->group_node); > > > } > > > cfs_rq->nr_queued--; > > > + > > > + /* safeguard to clear the cache aware data */ > > > + if (!parent_entity(se) && !cfs_rq->nr_queued) > > > + reset_llc_stats(rq_of(cfs_rq)); > >=20 > > Instead of relying on reset_llc_stats() hack, I think a better approach > > would be to have a "p->se.llc_sched_active" flag similar to how uclamp > > has "uc_se->active" and we set this in account_llc_enqueue() which will > > still check for sched_cache_enabled() but account_llc_dequeue() would > > only check for "p->se.llc_sched_active" to decrement the stats and then > > unset the flag. > >=20 > > That way, we cannot have an imbalanced accounting. Thoughts? > >=20 >=20 > I suppose what you mean is to avoid the race condition between > enabling sched_cache and EQ/DE_LLC, similar to uclamp: >=20 > enqueue(taskA) > // sched_cache gets enabled > enqueue(taskB) > dequeue(taskA) > // Must not decrement rq->llc_pref for taskA For this case, task A is already on rq when sched cache get enabled. But task A's preferred_llc is still -1.=20 If we dequeue it while its preferred_llc is still -1, it won't affect rq->llc_pref. If we change its preferred_llc to llc_i before we dequeue it, then rq->llc_pref[llc_i] will be incremented first. Then when we dequeue task A, we will decrement it. We are still accounting rq->llc_pref[llc_i] correctly with current code. The trickier case is if we need to dynamically resize rq->llc_pref[]. We need to make sure that we lock the rq to prevent enqueue/dequeue, switch it to a larger size rq->llc_pref[], copy the old data over, then switch over to the larger sized rq->llc_pref[] and unlock rq to keep the accounting straight. Tim=20 > dequeue(taskB) >=20 > We'll think more about this. >=20 > thanks, > Chenyu