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Commit a25707f3 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

sched: remove precise CPU load 



CPU load calculations are statistical anyway, and there's little benefit
from having it calculated on every scheduling event. So remove this code,
it gets rid of a divide from the scheduler wakeup and context-switch
fastpath.

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarMike Galbraith <efault@gmx.de>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 8ebc91d9

kernel/sched.c

+7 −35
Original line number Diff line number Diff line
@@ -1972,42 +1972,11 @@ unsigned long nr_active(void) 
 */

static void update_cpu_load(struct rq *this_rq)

{

	u64 fair_delta64, exec_delta64, idle_delta64, sample_interval64, tmp64;

	unsigned long total_load = this_rq->ls.load.weight;

	unsigned long this_load =  total_load;

	struct load_stat *ls = &this_rq->ls;

	int i, scale;



	this_rq->nr_load_updates++;

	if (unlikely(!(sysctl_sched_features & SCHED_FEAT_PRECISE_CPU_LOAD)))

		goto do_avg;



	/* Update delta_fair/delta_exec fields first */

	update_curr_load(this_rq);



	fair_delta64 = ls->delta_fair + 1;

	ls->delta_fair = 0;



	exec_delta64 = ls->delta_exec + 1;

	ls->delta_exec = 0;



	sample_interval64 = this_rq->clock - ls->load_update_last;

	ls->load_update_last = this_rq->clock;



	if ((s64)sample_interval64 < (s64)TICK_NSEC)

		sample_interval64 = TICK_NSEC;



	if (exec_delta64 > sample_interval64)

		exec_delta64 = sample_interval64;



	idle_delta64 = sample_interval64 - exec_delta64;



	tmp64 = div64_64(SCHED_LOAD_SCALE * exec_delta64, fair_delta64);

	tmp64 = div64_64(tmp64 * exec_delta64, sample_interval64);



	this_load = (unsigned long)tmp64;



do_avg:



	/* Update our load: */

	for (i = 0, scale = 1; i < CPU_LOAD_IDX_MAX; i++, scale += scale) {
@@ -2017,7 +1986,13 @@ static void update_cpu_load(struct rq *this_rq) 


		old_load = this_rq->cpu_load[i];

		new_load = this_load;



		/*

		 * Round up the averaging division if load is increasing. This

		 * prevents us from getting stuck on 9 if the load is 10, for

		 * example.

		 */

		if (new_load > old_load)

			new_load += scale-1;

		this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;

	}

}
@@ -6484,7 +6459,6 @@ static inline void init_cfs_rq(struct cfs_rq *cfs_rq, struct rq *rq) 


void __init sched_init(void)

{

	u64 now = sched_clock();

	int highest_cpu = 0;

	int i, j;
@@ -6509,8 +6483,6 @@ void __init sched_init(void) 
		INIT_LIST_HEAD(&rq->leaf_cfs_rq_list);

		list_add(&rq->cfs.leaf_cfs_rq_list, &rq->leaf_cfs_rq_list);

#endif

		rq->ls.load_update_last = now;

		rq->ls.load_update_start = now;



		for (j = 0; j < CPU_LOAD_IDX_MAX; j++)

			rq->cpu_load[j] = 0;

kernel/sched_debug.c

+0 −2
Original line number Diff line number Diff line
@@ -145,8 +145,6 @@ static void print_cpu(struct seq_file *m, int cpu) 
	P(nr_running);

	SEQ_printf(m, "  .%-30s: %lu\n", "load",

		   rq->ls.load.weight);

	P(ls.delta_fair);

	P(ls.delta_exec);

	P(nr_switches);

	P(nr_load_updates);

	P(nr_uninterruptible);

kernel/sched_fair.c

+2 −4
Original line number Diff line number Diff line
@@ -94,16 +94,14 @@ enum { 
	SCHED_FEAT_FAIR_SLEEPERS	= 1,

	SCHED_FEAT_SLEEPER_AVG		= 2,

	SCHED_FEAT_SLEEPER_LOAD_AVG	= 4,

	SCHED_FEAT_PRECISE_CPU_LOAD	= 8,

	SCHED_FEAT_START_DEBIT		= 16,

	SCHED_FEAT_SKIP_INITIAL		= 32,

	SCHED_FEAT_START_DEBIT		= 8,

	SCHED_FEAT_SKIP_INITIAL		= 16,

};



const_debug unsigned int sysctl_sched_features =

		SCHED_FEAT_FAIR_SLEEPERS	*1 |

		SCHED_FEAT_SLEEPER_AVG		*0 |

		SCHED_FEAT_SLEEPER_LOAD_AVG	*1 |

		SCHED_FEAT_PRECISE_CPU_LOAD	*1 |

		SCHED_FEAT_START_DEBIT		*1 |

		SCHED_FEAT_SKIP_INITIAL		*0;