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 DrFnQ0wu 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Kayra, On Fri, Sep 11, 2026 at 01:03:30AM +0300, Kayra Cizmeci wrote: > Hello Tim, > > > So moving the accounting next to (or after) the h_nr_runnable update > > would make task_pref_llc_runnable() return false and skip the > > decrement, leaving nr_pref_llc_running too high. > > What I really wanted wasn't getting the accounting next to or after the h_nr_runnable. > If we are updating h_nr_runnable in some way that means we don't need > its check since it's already getting updated. And if it's getting updated > that means on that branch we know how our check should behave since we > are a subset of it. We can skip the delayed check on that way since we are > trying to behave as h_nr_runnable's subset. > > > if (entity_is_task(se)) > > pref_llc_running_dec(...); /* sched_delayed still 0 */ > > se->sched_delayed = 1; > > ... > > for_each_sched_entity(se) > > cfs_rq->h_nr_runnable--; /* sched_delayed already 1 */ > > For example: > > In this code the h_nr_runnable is updated the same way regarding what is sched_delayed. > That means if we want to behave as a subset of it, we don't need the check delayed, > since we check the delayed to be a subset but if h_nr_runnable is decreasing/increasing > we should look into our checks. > I had a try according to your suggestion. It seems that the code becomes more complex and brings more headache :-( due to several corner cases. The current version is a simpler version with less code IMO. But I agree it looks a little hard to catch up with, so I added some comments around account_llc_dequeue() and adjusted the code sequence of clear_delayed() to make it easier to understand. Tim, could you please help check if this makes sense? diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e64d9ad7a108..89311bbadfac 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1609,8 +1609,58 @@ static void account_llc_dequeue(struct rq *rq, struct task_struct *p) if (p->pref_llc_queued) { /* * Skipped if still delayed (set_delayed() already removed it); - * clearing pref_llc_queued below also stops clear_delayed() - * from re-adding it. + * + * The nr_pref_llc_running varies with h_nr_runnable, it involves + * set_delayed(), clear_delayed(), account_llc_enqueued() and account_llc_dequeue(). + * The following shows two typical cases of how nr_pref_llc_running is maintained + * during enqueue/dequeue. + * + * case 1 - wakeup a delayed task + * + * CPU0 CPU1 + * __dequeue_task [fake dequeue] + * set_delayed + * rq0->nr_pref_llc_running-- + * p->se.sched_delayed = 1 + * + * try_to_wake_up(p) + * enqueue_task_fair + * requeue_delayed_entity + * clear_delayed + * rq0->nr_pref_llc_running++ + * + * + * case 2 - LB for delayed task + * + * CPU0 CPU1 + * __dequeue_task [fake dequeue] + * set_delayed + * rq0->nr_pref_llc_running-- + * p->se.sched_delayed = 1 + * + * + * --------- load balance --------- + * detach_task(p, rq0, migrate_load) + * account_llc_dequeue + * ** DO-NOT-DECREASE ** + * rq0->nr_pref_llc_running + * + * attach_task(p, rq1) + * account_llc_enqueue + * ** DO-NOT-INCREASE ** + * rq1->nr_pref_llc_running + * + * pick_eevdf + * __dequeue_task [real dequeue] + * account_llc_dequeue(DEQUEUE_DELAYED) + * ** DO-NOT-DECREASE ** + * rq1->nr_pref_llc_running + * p->pref_llc_queued = 0; + * + * clear_delayed + * p->se.sched_delayed = 0; + * ** DO-NOT-INCREASE as pref_llc_queued=0 ** + * rq1->nr_pref_llc_running */ pref_llc_running_dec(rq, p); /* @@ -6415,23 +6465,18 @@ static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq); static void set_delayed(struct sched_entity *se) { - /* - * Drop a task leaving the runnable set. Must run before sched_delayed - * is set, or task_pref_llc_runnable() would already exclude it; - * clear_delayed() mirrors this after clearing the flag. - */ - if (entity_is_task(se)) - pref_llc_running_dec(rq_of(cfs_rq_of(se)), task_of(se)); - - se->sched_delayed = 1; - /* * Delayed se of cfs_rq have no tasks queued on them. * Do not adjust h_nr_runnable since __dequeue_task() * will account it for blocked tasks. */ - if (!entity_is_task(se)) + if (!entity_is_task(se)) { + se->sched_delayed = 1; return; + } + + pref_llc_running_dec(rq_of(cfs_rq_of(se)), task_of(se)); + se->sched_delayed = 1; for_each_sched_entity(se) { struct cfs_rq *cfs_rq = cfs_rq_of(se); -- 2.43.0