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sched: avoid large irq-latencies in smp-balancing 

SMP balancing is done with IRQs disabled and can iterate the full rq.
When rqs are large this can cause large irq-latencies. Limit the nr of
iterations on each run.

This fixes a scheduling latency regression reported by the -rt folks.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2007-11-09 22:39:39 +01:00 committed by Ingo Molnar
parent 3c90e6e99b
commit b82d9fdd84
3 changed files with 19 additions and 5 deletions
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1
include/linux/sched.h
View File

@ -1466,6 +1466,7 @@ extern unsigned int sysctl_sched_batch_wakeup_granularity;
extern unsigned int sysctl_sched_child_runs_first;
extern unsigned int sysctl_sched_features;
extern unsigned int sysctl_sched_migration_cost;
extern unsigned int sysctl_sched_nr_migrate;
int sched_nr_latency_handler(struct ctl_table *table, int write,
struct file *file, void __user *buffer, size_t *length,

15
kernel/sched.c
View File

@ -471,6 +471,12 @@ const_debug unsigned int sysctl_sched_features =
#define sched_feat(x) (sysctl_sched_features & SCHED_FEAT_##x)
/*
* Number of tasks to iterate in a single balance run.
* Limited because this is done with IRQs disabled.
*/
const_debug unsigned int sysctl_sched_nr_migrate = 32;
/*
* For kernel-internal use: high-speed (but slightly incorrect) per-cpu
* clock constructed from sched_clock():
@ -2235,7 +2241,7 @@ balance_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
enum cpu_idle_type idle, int *all_pinned,
int *this_best_prio, struct rq_iterator *iterator)
{
int pulled = 0, pinned = 0, skip_for_load;
int loops = 0, pulled = 0, pinned = 0, skip_for_load;
struct task_struct *p;
long rem_load_move = max_load_move;
@ -2249,10 +2255,10 @@ balance_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
*/
p = iterator->start(iterator->arg);
next:
if (!p)
if (!p || loops++ > sysctl_sched_nr_migrate)
goto out;
/*
* To help distribute high priority tasks accross CPUs we don't
* To help distribute high priority tasks across CPUs we don't
* skip a task if it will be the highest priority task (i.e. smallest
* prio value) on its new queue regardless of its load weight
*/
@ -2269,8 +2275,7 @@ next:
rem_load_move -= p->se.load.weight;
/*
* We only want to steal up to the prescribed number of tasks
* and the prescribed amount of weighted load.
* We only want to steal up to the prescribed amount of weighted load.
*/
if (rem_load_move > 0) {
if (p->prio < *this_best_prio)

8
kernel/sysctl.c
View File

@ -301,6 +301,14 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
{
.ctl_name = CTL_UNNUMBERED,
.procname = "sched_nr_migrate",
.data = &sysctl_sched_nr_migrate,
.maxlen = sizeof(unsigned int),
.mode = 644,
.proc_handler = &proc_dointvec,
},
#endif
{
.ctl_name = CTL_UNNUMBERED,