struct worker_pool->nr_running

0.0.1. Defination

141 /* struct worker is defined in workqueue_internal.h */
142
143 struct worker_pool {
...
173         /*
174          * The current concurrency level.  As it's likely to be accessed
175          * from other CPUs during try_to_wake_up(), put it in a separate
176          * cacheline.
177          */
178         atomic_t                nr_running ____cacheline_aligned_in_smp;

0.0.2. Increase

813 /**
814  * wq_worker_waking_up - a worker is waking up
815  * @task: task waking up
816  * @cpu: CPU @task is waking up to
817  *
818  * This function is called during try_to_wake_up() when a worker is
819  * being awoken.
820  *
821  * CONTEXT:
822  * spin_lock_irq(rq->lock)
823  */
824 void wq_worker_waking_up(struct task_struct *task, int cpu)
825 {
826         struct worker *worker = kthread_data(task);
827
828         if (!(worker->flags & WORKER_NOT_RUNNING)) {
829                 WARN_ON_ONCE(worker->pool->cpu != cpu);
830                 atomic_inc(&worker->pool->nr_running);
831         }
832 }

923 /**
924  * worker_clr_flags - clear worker flags and adjust nr_running accordingly
925  * @worker: self
926  * @flags: flags to clear
927  *
928  * Clear @flags in @worker->flags and adjust nr_running accordingly.
929  *
930  * CONTEXT:
931  * spin_lock_irq(pool->lock)
932  */
933 static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
934 {
935         struct worker_pool *pool = worker->pool;
936         unsigned int oflags = worker->flags;
937
938         WARN_ON_ONCE(worker->task != current);
939
940         worker->flags &= ~flags;
941
942         /*
943          * If transitioning out of NOT_RUNNING, increment nr_running.  Note
944          * that the nested NOT_RUNNING is not a noop.  NOT_RUNNING is mask
945          * of multiple flags, not a single flag.
946          */
947         if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
948                 if (!(worker->flags & WORKER_NOT_RUNNING))
949                         atomic_inc(&pool->nr_running);
950 }

0.0.3. Decrease

885 /**
886  * worker_set_flags - set worker flags and adjust nr_running accordingly
887  * @worker: self
888  * @flags: flags to set
889  * @wakeup: wakeup an idle worker if necessary
890  *
891  * Set @flags in @worker->flags and adjust nr_running accordingly.  If
892  * nr_running becomes zero and @wakeup is %true, an idle worker is
893  * woken up.
894  *
895  * CONTEXT:
896  * spin_lock_irq(pool->lock)
897  */
898 static inline void worker_set_flags(struct worker *worker, unsigned int flags,
899                                     bool wakeup)
900 {
901         struct worker_pool *pool = worker->pool;
902
903         WARN_ON_ONCE(worker->task != current);
904
905         /*
906          * If transitioning into NOT_RUNNING, adjust nr_running and
907          * wake up an idle worker as necessary if requested by
908          * @wakeup.
909          */
910         if ((flags & WORKER_NOT_RUNNING) &&
911             !(worker->flags & WORKER_NOT_RUNNING)) {
912                 if (wakeup) {
913                         if (atomic_dec_and_test(&pool->nr_running) &&
914                             !list_empty(&pool->worklist))
915                                 wake_up_worker(pool);
916                 } else
917                         atomic_dec(&pool->nr_running);
918         }
919
920         worker->flags |= flags;
921 }

834 /**
835  * wq_worker_sleeping - a worker is going to sleep
836  * @task: task going to sleep
837  * @cpu: CPU in question, must be the current CPU number
838  *
839  * This function is called during schedule() when a busy worker is
840  * going to sleep.  Worker on the same cpu can be woken up by
841  * returning pointer to its task.
842  *
843  * CONTEXT:
844  * spin_lock_irq(rq->lock)
845  *
846  * Return:
847  * Worker task on @cpu to wake up, %NULL if none.
848  */
849 struct task_struct *wq_worker_sleeping(struct task_struct *task, int cpu)
850 {
851         struct worker *worker = kthread_data(task), *to_wakeup = NULL;
852         struct worker_pool *pool;
853
854         /*
855          * Rescuers, which may not have all the fields set up like normal
856          * workers, also reach here, let's not access anything before
857          * checking NOT_RUNNING.
858          */
859         if (worker->flags & WORKER_NOT_RUNNING)
860                 return NULL;
861
862         pool = worker->pool;
863
864         /* this can only happen on the local cpu */
865         if (WARN_ON_ONCE(cpu != raw_smp_processor_id()))
866                 return NULL;
867
868         /*
869          * The counterpart of the following dec_and_test, implied mb,
870          * worklist not empty test sequence is in insert_work().
871          * Please read comment there.
872          *
873          * NOT_RUNNING is clear.  This means that we're bound to and
874          * running on the local cpu w/ rq lock held and preemption
875          * disabled, which in turn means that none else could be
876          * manipulating idle_list, so dereferencing idle_list without pool
877          * lock is safe.
878          */
879         if (atomic_dec_and_test(&pool->nr_running) &&
880             !list_empty(&pool->worklist))
881                 to_wakeup = first_worker(pool);
882         return to_wakeup ? to_wakeup->task : NULL;
883 }