Commit 1799e35d authored by Ingo Molnar's avatar Ingo Molnar
Browse files

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: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
parent a88a8eff

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

kernel/sched.c

+1 −4
Original line number Diff line number Diff line
@@ -4550,9 +4550,6 @@ 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);



	/*

kernel/sched_fair.c

+57 −6
Original line number Diff line number Diff line
@@ -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)
@@ -897,12 +905,24 @@ 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;



	/*

	 * 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
@@ -910,6 +930,37 @@ static void yield_task_fair(struct rq *rq, struct task_struct *p) 
		 */

		dequeue_entity(cfs_rq, &p->se, 0);

		enqueue_entity(cfs_rq, &p->se, 0);



		return;

	}

	/*

	 * Find the rightmost entry in the rbtree:

	 */

	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);

}



/*

kernel/sysctl.c

+8 −0
Original line number Diff line number Diff line
@@ -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,

CRA Git | Maintained and supported by SUSTech CRA and CCSE