sched: refine negative nice level granularity

refine the granularity of negative nice level tasks: let them
reschedule more often to offset the effect of them consuming
their wait_runtime proportionately slower. (This makes nice-0
task scheduling smoother in the presence of negatively
reniced tasks.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 6 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 7a632c534ce5..e91db32cadfd 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -222,21 +222,25 @@ niced_granularity(struct sched_entity *curr, unsigned long granularity)
 {
         u64 tmp;
 
+        if (likely(curr->load.weight == NICE_0_LOAD))
+                return granularity;
         /*
-         * Negative nice levels get the same granularity as nice-0:
+         * Positive nice levels get the same granularity as nice-0:
          */
-        if (likely(curr->load.weight >= NICE_0_LOAD))
-                return granularity;
+        if (likely(curr->load.weight < NICE_0_LOAD)) {
+                tmp = curr->load.weight * (u64)granularity;
+                return (long) (tmp >> NICE_0_SHIFT);
+        }
         /*
-         * Positive nice level tasks get linearly finer
+         * Negative nice level tasks get linearly finer
          * granularity:
          */
-        tmp = curr->load.weight * (u64)granularity;
+        tmp = curr->load.inv_weight * (u64)granularity;
 
         /*
          * It will always fit into 'long':
          */
-        return (long) (tmp >> NICE_0_SHIFT);
+        return (long) (tmp >> WMULT_SHIFT);
 }
 
 static inline void