From f207dc2dcdcf0e1e7d260b392784855ce8d84147 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 27 Sep 2024 13:46:12 -1000 Subject: [PATCH] sched/core: Add ENQUEUE_RQ_SELECTED to indicate whether ->select_task_rq() was called During ttwu, ->select_task_rq() can be skipped if only one CPU is allowed or migration is disabled. sched_ext schedulers may perform operations such as direct dispatch from ->select_task_rq() path and it is useful for them to know whether ->select_task_rq() was skipped in the ->enqueue_task() path. Currently, sched_ext schedulers are using ENQUEUE_WAKEUP for this purpose and end up assuming incorrectly that ->select_task_rq() was called for tasks that are bound to a single CPU or migration disabled. Make select_task_rq() indicate whether ->select_task_rq() was called by setting WF_RQ_SELECTED in *wake_flags and make ttwu_do_activate() map that to ENQUEUE_RQ_SELECTED for ->enqueue_task(). This will be used by sched_ext to fix ->select_task_rq() skip detection. Signed-off-by: Tejun Heo Acked-by: David Vernet --- kernel/sched/core.c | 8 ++++++-- kernel/sched/sched.h | 3 +++ 2 files changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e70b57a5693ecf..aeb59551446193 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3522,10 +3522,12 @@ int select_task_rq(struct task_struct *p, int cpu, int *wake_flags) { lockdep_assert_held(&p->pi_lock); - if (p->nr_cpus_allowed > 1 && !is_migration_disabled(p)) + if (p->nr_cpus_allowed > 1 && !is_migration_disabled(p)) { cpu = p->sched_class->select_task_rq(p, cpu, *wake_flags); - else + *wake_flags |= WF_RQ_SELECTED; + } else { cpu = cpumask_any(p->cpus_ptr); + } /* * In order not to call set_task_cpu() on a blocking task we need @@ -3659,6 +3661,8 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags, rq->nr_uninterruptible--; #ifdef CONFIG_SMP + if (wake_flags & WF_RQ_SELECTED) + en_flags |= ENQUEUE_RQ_SELECTED; if (wake_flags & WF_MIGRATED) en_flags |= ENQUEUE_MIGRATED; else diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index b1c3588a8f0039..6085ef50febfaf 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2292,6 +2292,7 @@ static inline int task_on_rq_migrating(struct task_struct *p) #define WF_SYNC 0x10 /* Waker goes to sleep after wakeup */ #define WF_MIGRATED 0x20 /* Internal use, task got migrated */ #define WF_CURRENT_CPU 0x40 /* Prefer to move the wakee to the current CPU. */ +#define WF_RQ_SELECTED 0x80 /* ->select_task_rq() was called */ #ifdef CONFIG_SMP static_assert(WF_EXEC == SD_BALANCE_EXEC); @@ -2334,6 +2335,7 @@ extern const u32 sched_prio_to_wmult[40]; * ENQUEUE_HEAD - place at front of runqueue (tail if not specified) * ENQUEUE_REPLENISH - CBS (replenish runtime and postpone deadline) * ENQUEUE_MIGRATED - the task was migrated during wakeup + * ENQUEUE_RQ_SELECTED - ->select_task_rq() was called * */ @@ -2360,6 +2362,7 @@ extern const u32 sched_prio_to_wmult[40]; #define ENQUEUE_INITIAL 0x80 #define ENQUEUE_MIGRATING 0x100 #define ENQUEUE_DELAYED 0x200 +#define ENQUEUE_RQ_SELECTED 0x400 #define RETRY_TASK ((void *)-1UL)