Re: [patch] sched: disable task group re-weighting on the desktop

[Mike Galbraith <umgwanakikbuti@gmail.com>]

On Sat, 2015-10-10 at 22:03 +0800, kbuild test robot wrote:
> Hi Mike,

Hi there pin-the-tail-on-the-donkey bot.  Eeee Ahhh :)

sched: disable task group wide utilization based weight on the desktop

Task group wide utilization based weight may work well for servers, but it
is horrible on the desktop.  8 groups of 1 hog demoloshes interactivity, 1
group of 8 hogs has noticable impact, 2 such groups is very very noticable.

Turn it off if autogroup is enabled, and add a feature to let people set the
definition of fair to what serves them best.  For the desktop, fixed group
weight wins hands down, no contest....

Signed-off-by: Mike Galbraith <umgwanakikbuit@gmail.com>
---
 kernel/sched/fair.c     |    5 +++++
 kernel/sched/features.h |   14 ++++++++++++++

---
 kernel/sched/fair.c     |    5 +++++
 kernel/sched/features.h |   14 ++++++++++++++
 2 files changed, 19 insertions(+)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2372,6 +2372,8 @@ static long calc_cfs_shares(struct cfs_r
 {
 	long tg_weight, load, shares;
 
+	if (!sched_feat(SMP_FAIR_GROUPS))
+		return tg->shares;
 	tg_weight = calc_tg_weight(tg, cfs_rq);
 	load = cfs_rq_load_avg(cfs_rq);
 
@@ -2423,6 +2425,9 @@ static void update_cfs_shares(struct cfs
 #ifndef CONFIG_SMP
 	if (likely(se->load.weight == tg->shares))
 		return;
+#else
+	if (!sched_feat(SMP_FAIR_GROUPS) && se->load.weight == tg->shares)
+		return;
 #endif
 	shares = calc_cfs_shares(cfs_rq, tg);
 
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -88,3 +88,17 @@ SCHED_FEAT(LB_MIN, false)
  */
 SCHED_FEAT(NUMA,	true)
 #endif
+
+#ifdef CONFIG_FAIR_GROUP_SCHED
+/*
+ * With SMP_FAIR_GROUPS set, activity group wide determines share for
+ * all froup members.  This does very bad things to interactivity when
+ * a desktop box is heavily loaded.  Default to off when autogroup is
+ * enabled, and let all users set it to what works best for them.
+ */
+#if defined(CONFIG_SMP) && defined(CONFIG_FAIR_GROUP_SCHED)
+SCHED_FEAT(SMP_FAIR_GROUPS, true)
+#else
+SCHED_FEAT(SMP_FAIR_GROUPS, false)
+#endif
+#endif