From 1799e35d5baab6e06168b46cc78b968e728ea3d1 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Wed, 19 Sep 2007 23:34:46 +0200 Subject: [PATCH] sched: add /proc/sys/kernel/sched_compat_yield add /proc/sys/kernel/sched_compat_yield to make sys_sched_yield() more agressive, by moving the yielding task to the last position in the rbtree. with sched_compat_yield=0: PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 2539 mingo 20 0 1576 252 204 R 50 0.0 0:02.03 loop_yield 2541 mingo 20 0 1576 244 196 R 50 0.0 0:02.05 loop with sched_compat_yield=1: PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 2584 mingo 20 0 1576 248 196 R 99 0.0 0:52.45 loop 2582 mingo 20 0 1576 256 204 R 0 0.0 0:00.00 loop_yield Signed-off-by: Ingo Molnar Signed-off-by: Peter Zijlstra --- include/linux/sched.h | 1 + kernel/sched.c | 5 +--- kernel/sched_fair.c | 63 ++++++++++++++++++++++++++++++++++++++----- kernel/sysctl.c | 8 ++++++ 4 files changed, 67 insertions(+), 10 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 5445eaec6908..3de79016f2a6 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1406,6 +1406,7 @@ extern unsigned int sysctl_sched_wakeup_granularity; extern unsigned int sysctl_sched_batch_wakeup_granularity; extern unsigned int sysctl_sched_stat_granularity; extern unsigned int sysctl_sched_runtime_limit; +extern unsigned int sysctl_sched_compat_yield; extern unsigned int sysctl_sched_child_runs_first; extern unsigned int sysctl_sched_features; diff --git a/kernel/sched.c b/kernel/sched.c index deeb1f8e0c30..63e0971c8fbb 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -4550,10 +4550,7 @@ asmlinkage long sys_sched_yield(void) struct rq *rq = this_rq_lock(); schedstat_inc(rq, yld_cnt); - if (unlikely(rq->nr_running == 1)) - schedstat_inc(rq, yld_act_empty); - else - current->sched_class->yield_task(rq, current); + current->sched_class->yield_task(rq, current); /* * Since we are going to call schedule() anyway, there's diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 892616bf2c77..c9fbe8e73a45 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -42,6 +42,14 @@ unsigned int sysctl_sched_latency __read_mostly = 20000000ULL; */ unsigned int sysctl_sched_min_granularity __read_mostly = 2000000ULL; +/* + * sys_sched_yield() compat mode + * + * This option switches the agressive yield implementation of the + * old scheduler back on. + */ +unsigned int __read_mostly sysctl_sched_compat_yield; + /* * SCHED_BATCH wake-up granularity. * (default: 25 msec, units: nanoseconds) @@ -897,19 +905,62 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int sleep) } /* - * sched_yield() support is very simple - we dequeue and enqueue + * sched_yield() support is very simple - we dequeue and enqueue. + * + * If compat_yield is turned on then we requeue to the end of the tree. */ static void yield_task_fair(struct rq *rq, struct task_struct *p) { struct cfs_rq *cfs_rq = task_cfs_rq(p); + struct rb_node **link = &cfs_rq->tasks_timeline.rb_node; + struct sched_entity *rightmost, *se = &p->se; + struct rb_node *parent; - __update_rq_clock(rq); /* - * Dequeue and enqueue the task to update its - * position within the tree: + * Are we the only task in the tree? + */ + if (unlikely(cfs_rq->nr_running == 1)) + return; + + if (likely(!sysctl_sched_compat_yield)) { + __update_rq_clock(rq); + /* + * Dequeue and enqueue the task to update its + * position within the tree: + */ + dequeue_entity(cfs_rq, &p->se, 0); + enqueue_entity(cfs_rq, &p->se, 0); + + return; + } + /* + * Find the rightmost entry in the rbtree: */ - dequeue_entity(cfs_rq, &p->se, 0); - enqueue_entity(cfs_rq, &p->se, 0); + do { + parent = *link; + link = &parent->rb_right; + } while (*link); + + rightmost = rb_entry(parent, struct sched_entity, run_node); + /* + * Already in the rightmost position? + */ + if (unlikely(rightmost == se)) + return; + + /* + * Minimally necessary key value to be last in the tree: + */ + se->fair_key = rightmost->fair_key + 1; + + if (cfs_rq->rb_leftmost == &se->run_node) + cfs_rq->rb_leftmost = rb_next(&se->run_node); + /* + * Relink the task to the rightmost position: + */ + rb_erase(&se->run_node, &cfs_rq->tasks_timeline); + rb_link_node(&se->run_node, parent, link); + rb_insert_color(&se->run_node, &cfs_rq->tasks_timeline); } /* diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 6ace893c17c9..53a456ebf6d5 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -303,6 +303,14 @@ static ctl_table kern_table[] = { .proc_handler = &proc_dointvec, }, #endif + { + .ctl_name = CTL_UNNUMBERED, + .procname = "sched_compat_yield", + .data = &sysctl_sched_compat_yield, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = &proc_dointvec, + }, #ifdef CONFIG_PROVE_LOCKING { .ctl_name = CTL_UNNUMBERED, -- 2.20.1