linux-kernel - [PATCH RESEND v2 6/6] sched/fair: Remove unconditionally inactive code

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Message-Id: <1459369015-28375-7-git-send-email-yuyang.du@intel.com>
Date:	Thu, 31 Mar 2016 04:16:55 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	peterz@...radead.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org
Cc:	bsegall@...gle.com, pjt@...gle.com, morten.rasmussen@....com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	lizefan@...wei.com, umgwanakikbuti@...il.com,
	Yuyang Du <yuyang.du@...el.com>
Subject: [PATCH RESEND v2 6/6] sched/fair: Remove unconditionally inactive code

The increased load resolution (fixed point arithmetic range) is
unconditionally deactivated with #if 0, so it is effectively broken.

But the increased load range is still used somewhere (e.g., in Google),
so we keep this feature. The reconciliation is we define
CONFIG_CFS_INCREASE_LOAD_RANGE and it depends on FAIR_GROUP_SCHED and
64BIT and BROKEN.

Suggested-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Yuyang Du <yuyang.du@...el.com>
---
 init/Kconfig         | 16 +++++++++++++++
 kernel/sched/sched.h | 55 +++++++++++++++++++++-------------------------------
 2 files changed, 38 insertions(+), 33 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 2232080..d072c09 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1025,6 +1025,22 @@ config CFS_BANDWIDTH
 	  restriction.
 	  See tip/Documentation/scheduler/sched-bwc.txt for more information.
 
+config CFS_INCREASE_LOAD_RANGE
+	bool "Increase kernel load range"
+	depends on 64BIT && BROKEN
+	default n
+	help
+	  Increase resolution of nice-level calculations for 64-bit architectures.
+	  The extra resolution improves shares distribution and load balancing of
+	  low-weight task groups (eg. nice +19 on an autogroup), deeper taskgroup
+	  hierarchies, especially on larger systems. This is not a user-visible change
+	  and does not change the user-interface for setting shares/weights.
+	  We increase resolution only if we have enough bits to allow this increased
+	  resolution (i.e. BITS_PER_LONG > 32). The costs for increasing resolution
+	  when BITS_PER_LONG <= 32 are pretty high and the returns do not justify the
+	  increased costs.
+	  Currently broken: it increases power usage under light load.
+
 config RT_GROUP_SCHED
 	bool "Group scheduling for SCHED_RR/FIFO"
 	depends on CGROUP_SCHED
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ebe16e3..1bb0d69 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -42,39 +42,6 @@ static inline void update_cpu_load_active(struct rq *this_rq) { }
 #define NS_TO_JIFFIES(TIME)	((unsigned long)(TIME) / (NSEC_PER_SEC / HZ))
 
 /*
- * Increase resolution of nice-level calculations for 64-bit architectures.
- * The extra resolution improves shares distribution and load balancing of
- * low-weight task groups (eg. nice +19 on an autogroup), deeper taskgroup
- * hierarchies, especially on larger systems. This is not a user-visible change
- * and does not change the user-interface for setting shares/weights.
- *
- * We increase resolution only if we have enough bits to allow this increased
- * resolution (i.e. BITS_PER_LONG > 32). The costs for increasing resolution
- * when BITS_PER_LONG <= 32 are pretty high and the returns do not justify the
- * increased costs.
- */
-#if 0 /* BITS_PER_LONG > 32 -- currently broken: it increases power usage under light load  */
-# define NICE_0_LOAD_SHIFT	(SCHED_FIXEDPOINT_SHIFT + SCHED_FIXEDPOINT_SHIFT)
-# define user_to_kernel_load(w)	((w) << SCHED_FIXEDPOINT_SHIFT)
-# define kernel_to_user_load(w)	((w) >> SCHED_FIXEDPOINT_SHIFT)
-#else
-# define NICE_0_LOAD_SHIFT	(SCHED_FIXEDPOINT_SHIFT)
-# define user_to_kernel_load(w)	(w)
-# define kernel_to_user_load(w)	(w)
-#endif
-
-/*
- * Task weight (visible to user) and its load (invisible to user) have
- * independent resolution, but they should be well calibrated. We use
- * user_to_kernel_load() and kernel_to_user_load(w) to convert between
- * them. The following must be true:
- *
- * user_to_kernel_load(sched_prio_to_weight[USER_PRIO(NICE_TO_PRIO(0))]) == NICE_0_LOAD
- * kernel_to_user_load(NICE_0_LOAD) == sched_prio_to_weight[USER_PRIO(NICE_TO_PRIO(0))]
- */
-#define NICE_0_LOAD		(1L << NICE_0_LOAD_SHIFT)
-
-/*
  * Single value that decides SCHED_DEADLINE internal math precision.
  * 10 -> just above 1us
  * 9  -> just above 0.5us
@@ -1150,6 +1117,28 @@ extern const int sched_prio_to_weight[40];
 extern const u32 sched_prio_to_wmult[40];
 
 /*
+ * Task weight (visible to user) and its load (invisible to user) have
+ * independent ranges, but they should be well calibrated. We use
+ * user_to_kernel_load() and kernel_to_user_load(w) to convert between
+ * them.
+ *
+ * The following must also be true:
+ * user_to_kernel_load(sched_prio_to_weight[USER_PRIO(NICE_TO_PRIO(0))]) == NICE_0_LOAD
+ * kernel_to_user_load(NICE_0_LOAD) == sched_prio_to_weight[USER_PRIO(NICE_TO_PRIO(0))]
+ */
+#ifdef CONFIG_CFS_INCREASE_LOAD_RANGE
+#define NICE_0_LOAD_SHIFT	(SCHED_FIXEDPOINT_SHIFT + SCHED_FIXEDPOINT_SHIFT)
+#define user_to_kernel_load(w)	(w << SCHED_FIXEDPOINT_SHIFT)
+#define kernel_to_user_load(w)	(w >> SCHED_FIXEDPOINT_SHIFT)
+#else
+#define NICE_0_LOAD_SHIFT	(SCHED_FIXEDPOINT_SHIFT)
+#define user_to_kernel_load(w)	(w)
+#define kernel_to_user_load(w)	(w)
+#endif
+
+#define NICE_0_LOAD		(1UL << NICE_0_LOAD_SHIFT)
+
+/*
  * {de,en}queue flags:
  *
  * DEQUEUE_SLEEP  - task is no longer runnable
-- 
2.1.4