sched: adaptive scheduler granularity

Instead of specifying the preemption granularity, specify the wanted
latency. By fixing the granlarity to a constany the wakeup latency
it a function of the number of running tasks on the rq.

Invert this relation.

sysctl_sched_granularity becomes a minimum for the dynamic granularity
computed from the new sysctl_sched_latency.

Then use this latency to do more intelligent granularity decisions: if
there are fewer tasks running then we can schedule coarser. This helps
performance while still always keeping the latency target.

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

1 files changed, 11 insertions, 0 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index ea90ef51085c..9e3d2960faf5 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -233,6 +233,17 @@ static ctl_table kern_table[] = {
         },
         {
                 .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "sched_latency_ns",
+                .data           = &sysctl_sched_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,
+        },
+        {
+                .ctl_name       = CTL_UNNUMBERED,
                 .procname       = "sched_wakeup_granularity_ns",
                 .data           = &sysctl_sched_wakeup_granularity,
                 .maxlen         = sizeof(unsigned int),