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>

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 7a632c5..e91db32 100644 (file)
--- 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