sched: reintroduce the sched_min_granularity tunable
we lost the sched_min_granularity tunable to a clever optimization
that uses the sched_latency/min_granularity ratio - but the ratio
is quite unintuitive to users and can also crash the kernel if the
ratio is set to 0. So reintroduce the min_granularity tunable,
while keeping the ratio maintained internally.
no functionality changed.
[ mingo@elte.hu: some fixlets. ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 155d743..5457b62 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1460,12 +1460,16 @@
#ifdef CONFIG_SCHED_DEBUG
extern unsigned int sysctl_sched_latency;
-extern unsigned int sysctl_sched_nr_latency;
+extern unsigned int sysctl_sched_min_granularity;
extern unsigned int sysctl_sched_wakeup_granularity;
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;
+
+int sched_nr_latency_handler(struct ctl_table *table, int write,
+ struct file *file, void __user *buffer, size_t *length,
+ loff_t *ppos);
#endif
extern unsigned int sysctl_sched_compat_yield;
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index 415e5c3..ca198a7 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -211,7 +211,7 @@
#define PN(x) \
SEQ_printf(m, " .%-40s: %Ld.%06ld\n", #x, SPLIT_NS(x))
PN(sysctl_sched_latency);
- PN(sysctl_sched_nr_latency);
+ PN(sysctl_sched_min_granularity);
PN(sysctl_sched_wakeup_granularity);
PN(sysctl_sched_batch_wakeup_granularity);
PN(sysctl_sched_child_runs_first);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 8763bee..c495dcf 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -35,18 +35,23 @@
const_debug unsigned int sysctl_sched_latency = 20000000ULL;
/*
+ * Minimal preemption granularity for CPU-bound tasks:
+ * (default: 1 msec, units: nanoseconds)
+ */
+const_debug unsigned int sysctl_sched_min_granularity = 1000000ULL;
+
+/*
+ * is kept at sysctl_sched_latency / sysctl_sched_min_granularity
+ */
+const_debug unsigned int sched_nr_latency = 20;
+
+/*
* After fork, child runs first. (default) If set to 0 then
* parent will (try to) run first.
*/
const_debug unsigned int sysctl_sched_child_runs_first = 1;
/*
- * Minimal preemption granularity for CPU-bound tasks:
- * (default: 2 msec, units: nanoseconds)
- */
-const_debug unsigned int sysctl_sched_nr_latency = 20;
-
-/*
* sys_sched_yield() compat mode
*
* This option switches the agressive yield implementation of the
@@ -212,6 +217,22 @@
* Scheduling class statistics methods:
*/
+#ifdef CONFIG_SCHED_DEBUG
+int sched_nr_latency_handler(struct ctl_table *table, int write,
+ struct file *filp, void __user *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ int ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);
+
+ if (ret || !write)
+ return ret;
+
+ sched_nr_latency = DIV_ROUND_UP(sysctl_sched_latency,
+ sysctl_sched_min_granularity);
+
+ return 0;
+}
+#endif
/*
* The idea is to set a period in which each task runs once.
@@ -224,7 +245,7 @@
static u64 __sched_period(unsigned long nr_running)
{
u64 period = sysctl_sched_latency;
- unsigned long nr_latency = sysctl_sched_nr_latency;
+ unsigned long nr_latency = sched_nr_latency;
if (unlikely(nr_running > nr_latency)) {
period *= nr_running;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 3b4efbe..6e3b63c 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -235,11 +235,14 @@
#ifdef CONFIG_SCHED_DEBUG
{
.ctl_name = CTL_UNNUMBERED,
- .procname = "sched_nr_latency",
- .data = &sysctl_sched_nr_latency,
+ .procname = "sched_min_granularity_ns",
+ .data = &sysctl_sched_min_granularity,
.maxlen = sizeof(unsigned int),
.mode = 0644,
- .proc_handler = &proc_dointvec,
+ .proc_handler = &sched_nr_latency_handler,
+ .strategy = &sysctl_intvec,
+ .extra1 = &min_sched_granularity_ns,
+ .extra2 = &max_sched_granularity_ns,
},
{
.ctl_name = CTL_UNNUMBERED,
@@ -247,7 +250,7 @@
.data = &sysctl_sched_latency,
.maxlen = sizeof(unsigned int),
.mode = 0644,
- .proc_handler = &proc_dointvec_minmax,
+ .proc_handler = &sched_nr_latency_handler,
.strategy = &sysctl_intvec,
.extra1 = &min_sched_granularity_ns,
.extra2 = &max_sched_granularity_ns,
