Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=b82d9fdd848abfbe7263a4ecd9bbb55e575100a6
Commit: b82d9fdd848abfbe7263a4ecd9bbb55e575100a6
Parent: 3c90e6e99b08f01d5684a3a07cceae6a543e4fa8
Author: Peter Zijlstra <[EMAIL PROTECTED]>
AuthorDate: Fri Nov 9 22:39:39 2007 +0100
Committer: Ingo Molnar <[EMAIL PROTECTED]>
CommitDate: Fri Nov 9 22:39:39 2007 +0100
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 <[EMAIL PROTECTED]>
Acked-by: Steven Rostedt <[EMAIL PROTECTED]>
Tested-by: Gregory Haskins <[EMAIL PROTECTED]>
Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]>
---
include/linux/sched.h | 1 +
kernel/sched.c | 15 ++++++++++-----
kernel/sysctl.c | 8 ++++++++
3 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 93fd30d..2cc789f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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,
diff --git a/kernel/sched.c b/kernel/sched.c
index 2a107e4..e195a42 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -472,6 +472,12 @@ 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)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index adddf68..3a1744f 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -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,
-
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