sched: reintroduce cache-hot affinity
reintroduce a simplified version of cache-hot/cold scheduling
affinity. This improves performance with certain SMP workloads,
such as sysbench.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8be5b57..fcc9a5a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1415,6 +1415,7 @@
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;
#endif
extern unsigned int sysctl_sched_compat_yield;
diff --git a/kernel/sched.c b/kernel/sched.c
index 791dd08..089d8b1 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2119,6 +2119,17 @@
}
/*
+ * Is this task likely cache-hot:
+ */
+static inline int
+task_hot(struct task_struct *p, unsigned long long now, struct sched_domain *sd)
+{
+ s64 delta = now - p->se.exec_start;
+
+ return delta < (long long)sysctl_sched_migration_cost;
+}
+
+/*
* can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
*/
static
@@ -2139,6 +2150,22 @@
if (task_running(rq, p))
return 0;
+ /*
+ * Aggressive migration if:
+ * 1) task is cache cold, or
+ * 2) too many balance attempts have failed.
+ */
+
+ if (sd->nr_balance_failed > sd->cache_nice_tries) {
+#ifdef CONFIG_SCHEDSTATS
+ if (task_hot(p, rq->clock, sd))
+ schedstat_inc(sd, lb_hot_gained[idle]);
+#endif
+ return 1;
+ }
+
+ if (task_hot(p, rq->clock, sd))
+ return 0;
return 1;
}
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index cea1fa3..a17b785 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -74,6 +74,8 @@
*/
const_debug unsigned int sysctl_sched_wakeup_granularity = 10000000UL;
+const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
+
/**************************************************************
* CFS operations on generic schedulable entities:
*/
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 230ca4e..ec14aa8 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -277,6 +277,14 @@
.mode = 0644,
.proc_handler = &proc_dointvec,
},
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "sched_migration_cost",
+ .data = &sysctl_sched_migration_cost,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
#endif
{
.ctl_name = CTL_UNNUMBERED,