sched: fix calc_delta_asym()

calc_delta_asym() is supposed to do the same as calc_delta_fair() except
linearly shrink the result for negative nice processes - this causes them
to have a smaller preemption threshold so that they are more easily preempted.

The problem is that for task groups se->load.weight is the per cpu share of
the actual task group weight; take that into account.

Also provide a debug switch to disable the asymmetry (which I still don't
like - but it does greatly benefit some workloads)

This would explain the interactivity issues reported against group scheduling.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 28 insertions, 1 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 496500988ce5..2268e634812b 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -430,6 +430,29 @@ calc_delta_asym(unsigned long delta, struct sched_entity *se)
         for_each_sched_entity(se) {
                 struct load_weight *se_lw = &se->load;
 
+#ifdef CONFIG_FAIR_SCHED_GROUP
+                struct cfs_rq *cfs_rq = se->my_q;
+                struct task_group *tg = NULL
+
+                if (cfs_rq)
+                        tg = cfs_rq->tg;
+
+                if (tg && tg->shares < NICE_0_LOAD) {
+                        /*
+                         * scale shares to what it would have been had
+                         * tg->weight been NICE_0_LOAD:
+                         *
+                         *   weight = 1024 * shares / tg->weight
+                         */
+                        lw.weight *= se->load.weight;
+                        lw.weight /= tg->shares;
+
+                        lw.inv_weight = 0;
+
+                        se_lw = &lw;
+                } else
+#endif
+
                 if (se->load.weight < NICE_0_LOAD)
                         se_lw = &lw;
 
@@ -1154,7 +1177,10 @@ static unsigned long wakeup_gran(struct sched_entity *se)
          * More easily preempt - nice tasks, while not making it harder for
          * + nice tasks.
          */
-        gran = calc_delta_asym(sysctl_sched_wakeup_granularity, se);
+        if (sched_feat(ASYM_GRAN))
+                gran = calc_delta_asym(sysctl_sched_wakeup_granularity, se);
+        else
+                gran = calc_delta_fair(sysctl_sched_wakeup_granularity, se);
 
         return gran;
 }
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index afa549166d8d..04123af2e678 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -7,3 +7,4 @@ SCHED_FEAT(CACHE_HOT_BUDDY, 1)
 SCHED_FEAT(SYNC_WAKEUPS, 1)
 SCHED_FEAT(HRTICK, 1)
 SCHED_FEAT(DOUBLE_TICK, 0)
+SCHED_FEAT(ASYM_GRAN, 1)