sched: speed up and simplify vslice calculations

speed up and simplify vslice calculations.

[ From: Mike Galbraith <efault@gmx.de>: build fix ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 13 insertions, 13 deletions

diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index be79cd6d9e80..995bbd384a97 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -210,7 +210,7 @@ static int sched_debug_show(struct seq_file *m, void *v)
 #define PN(x) \
         SEQ_printf(m, "  .%-40s: %Ld.%06ld\n", #x, SPLIT_NS(x))
         PN(sysctl_sched_latency);
-        PN(sysctl_sched_min_granularity);
+        PN(sysctl_sched_nr_latency);
         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 ec0569e59e24..ae2d4b08e782 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -46,7 +46,7 @@ const_debug unsigned int sysctl_sched_child_runs_first = 1;
  * Minimal preemption granularity for CPU-bound tasks:
  * (default: 2 msec, units: nanoseconds)
  */
-unsigned int sysctl_sched_min_granularity __read_mostly = 2000000ULL;
+const_debug unsigned int sysctl_sched_nr_latency = 20;
 
 /*
  * sys_sched_yield() compat mode
@@ -222,8 +222,7 @@ static inline struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
 static u64 __sched_period(unsigned long nr_running)
 {
         u64 period = sysctl_sched_latency;
-        unsigned long nr_latency =
-                sysctl_sched_latency / sysctl_sched_min_granularity;
+        unsigned long nr_latency = sysctl_sched_nr_latency;
 
         if (unlikely(nr_running > nr_latency)) {
                 period *= nr_running;
@@ -245,11 +244,15 @@ static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 
 static u64 __sched_vslice(unsigned long nr_running)
 {
-        u64 period = __sched_period(nr_running);
+        unsigned long period = sysctl_sched_latency;
+        unsigned long nr_latency = sysctl_sched_nr_latency;
 
-        do_div(period, nr_running);
+        if (unlikely(nr_running > nr_latency))
+                nr_running = nr_latency;
 
-        return period;
+        period /= nr_running;
+
+        return (u64)period;
 }
 
 /*
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 97b15c27407f..230ca4eb57fe 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -222,14 +222,11 @@ static ctl_table kern_table[] = {
 #ifdef CONFIG_SCHED_DEBUG
         {
                 .ctl_name       = CTL_UNNUMBERED,
-                .procname       = "sched_min_granularity_ns",
-                .data           = &sysctl_sched_min_granularity,
+                .procname       = "sched_nr_latency",
+                .data           = &sysctl_sched_nr_latency,
                 .maxlen         = sizeof(unsigned int),
                 .mode           = 0644,
-                .proc_handler   = &proc_dointvec_minmax,
-                .strategy       = &sysctl_intvec,
-                .extra1         = &min_sched_granularity_ns,
-                .extra2         = &max_sched_granularity_ns,
+                .proc_handler   = &proc_dointvec,
         },
         {
                 .ctl_name       = CTL_UNNUMBERED,