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Date: Wed, 07 Nov 2007 13:17:00 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Ingo Molnar <mingo@...e.hu>
Cc: Peter Williams <pwil3058@...pond.net.au>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: avoid large irq-latencies in smp-balancing
Bah, missed a hunk
---
Subject: 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.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC: Peter Williams <pwil3058@...pond.net.au>
---
include/linux/sched.h | 1 +
kernel/sched.c | 15 ++++++++++-----
kernel/sysctl.c | 8 ++++++++
3 files changed, 19 insertions(+), 5 deletions(-)
Index: linux-2.6-2/kernel/sched.c
===================================================================
--- linux-2.6-2.orig/kernel/sched.c
+++ linux-2.6-2/kernel/sched.c
@@ -474,6 +474,12 @@ const_debug unsigned int sysctl_sched_fe
#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():
*/
@@ -2237,7 +2243,7 @@ balance_tasks(struct rq *this_rq, int th
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;
@@ -2251,10 +2257,10 @@ balance_tasks(struct rq *this_rq, int th
*/
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
*/
@@ -2271,8 +2277,7 @@ 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)
Index: linux-2.6-2/kernel/sysctl.c
===================================================================
--- linux-2.6-2.orig/kernel/sysctl.c
+++ linux-2.6-2/kernel/sysctl.c
@@ -298,6 +298,14 @@ 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,
Index: linux-2.6-2/include/linux/sched.h
===================================================================
--- linux-2.6-2.orig/include/linux/sched.h
+++ linux-2.6-2/include/linux/sched.h
@@ -1466,6 +1466,7 @@ extern unsigned int sysctl_sched_batch_w
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;
#endif
extern unsigned int sysctl_sched_compat_yield;
-
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