Add a yield_to function to the scheduler code, allowing us to give the remainder of our timeslice to another thread.
We may want to use this to provide a sys_yield_to system call one day. Signed-off-by: Rik van Riel <[email protected]> Signed-off-by: Marcelo Tosatti <[email protected]> --- - move to a per sched class yield_to - fix the locking diff --git a/include/linux/sched.h b/include/linux/sched.h index 2c79e92..408326f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1086,6 +1086,8 @@ struct sched_class { #ifdef CONFIG_FAIR_GROUP_SCHED void (*task_move_group) (struct task_struct *p, int on_rq); #endif + + void (*yield_to) (struct rq *rq, struct task_struct *p); }; struct load_weight { @@ -1947,6 +1949,7 @@ extern void set_user_nice(struct task_struct *p, long nice); extern int task_prio(const struct task_struct *p); extern int task_nice(const struct task_struct *p); extern int can_nice(const struct task_struct *p, const int nice); +extern void requeue_task(struct rq *rq, struct task_struct *p); extern int task_curr(const struct task_struct *p); extern int idle_cpu(int cpu); extern int sched_setscheduler(struct task_struct *, int, struct sched_param *); @@ -2020,6 +2023,10 @@ extern int wake_up_state(struct task_struct *tsk, unsigned int state); extern int wake_up_process(struct task_struct *tsk); extern void wake_up_new_task(struct task_struct *tsk, unsigned long clone_flags); + +extern u64 slice_remain(struct task_struct *); +extern void yield_to(struct task_struct *); + #ifdef CONFIG_SMP extern void kick_process(struct task_struct *tsk); #else diff --git a/kernel/sched.c b/kernel/sched.c index dc91a4d..6399641 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -5166,6 +5166,46 @@ SYSCALL_DEFINE3(sched_getaffinity, pid_t, pid, unsigned int, len, return ret; } +/* + * Yield the CPU, giving the remainder of our time slice to task p. + * Typically used to hand CPU time to another thread inside the same + * process, eg. when p holds a resource other threads are waiting for. + * Giving priority to p may help get that resource released sooner. + */ +void yield_to(struct task_struct *p) +{ + unsigned long flags; + struct rq *rq, *p_rq; + + local_irq_save(flags); + rq = this_rq(); +again: + p_rq = task_rq(p); + double_rq_lock(rq, p_rq); + if (p_rq != task_rq(p)) { + double_rq_unlock(rq, p_rq); + goto again; + } + + /* We can't yield to a process that doesn't want to run. */ + if (!p->se.on_rq) + goto out; + + /* + * We can only yield to a runnable task, in the same schedule class + * as the current task, if the schedule class implements yield_to_task. + */ + if (!task_running(rq, p) && current->sched_class == p->sched_class && + current->sched_class->yield_to) + current->sched_class->yield_to(rq, p); + +out: + double_rq_unlock(rq, p_rq); + local_irq_restore(flags); + yield(); +} +EXPORT_SYMBOL_GPL(yield_to); + /** * sys_sched_yield - yield the current processor to other threads. * diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 00ebd76..d8c4116 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -980,6 +980,25 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued) * CFS operations on tasks: */ +u64 slice_remain(struct task_struct *p) +{ + unsigned long flags; + struct sched_entity *se = &p->se; + struct cfs_rq *cfs_rq; + struct rq *rq; + u64 slice, ran; + s64 delta; + + rq = task_rq_lock(p, &flags); + cfs_rq = cfs_rq_of(se); + slice = sched_slice(cfs_rq, se); + ran = se->sum_exec_runtime - se->prev_sum_exec_runtime; + delta = slice - ran; + task_rq_unlock(rq, &flags); + + return max(delta, 0LL); +} + #ifdef CONFIG_SCHED_HRTICK static void hrtick_start_fair(struct rq *rq, struct task_struct *p) { @@ -1126,6 +1145,20 @@ static void yield_task_fair(struct rq *rq) se->vruntime = rightmost->vruntime + 1; } +static void yield_to_fair(struct rq *rq, struct task_struct *p) +{ + struct sched_entity *se = &p->se; + struct cfs_rq *cfs_rq = cfs_rq_of(se); + u64 remain = slice_remain(current); + + dequeue_task(rq, p, 0); + se->vruntime -= remain; + if (se->vruntime < cfs_rq->min_vruntime) + se->vruntime = cfs_rq->min_vruntime; + enqueue_task(rq, p, 0); + check_preempt_curr(rq, p, 0); +} + #ifdef CONFIG_SMP static void task_waking_fair(struct rq *rq, struct task_struct *p) @@ -3962,6 +3995,8 @@ static const struct sched_class fair_sched_class = { #ifdef CONFIG_FAIR_GROUP_SCHED .task_move_group = task_move_group_fair, #endif + + .yield_to = yield_to_fair, }; #ifdef CONFIG_SCHED_DEBUG -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
