sched: walt: Correct WALT window size initialization

It is preferable that WALT window rollover occurs just
before a tick, since the tick is an opportune moment
to record a complete window's statistics, as well as report
those stats to the cpu frequency governor. When CONFIG_HZ
results in a TICK_NSEC that isn't a integral number, this
requirement may be violated. Account for this by reducing
the WALT window size to the nearest multiple of TICK_NSEC.

Commit d368c6f ("sched: walt: fix window misalignment
when HZ=300") attempted to do this but WALT isn't using
MIN_SCHED_RAVG_WINDOW as the window size and the patch was
doing nothing.

Also, change the type of 'walt_disabled' to bool and warn
if an invalid window size causes WALT to be disabled.

Change-Id: Ie3dcfc21a3df4408254ca1165a355bbe391ed5c7
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>

Author: Vikram Mulukutla

include/trace/events/sched.h

@@ -642,7 +642,7 @@ TRACE_EVENT(sched_contrib_scale_f,
 extern unsigned int sysctl_sched_use_walt_cpu_util;
 extern unsigned int sysctl_sched_use_walt_task_util;
 extern unsigned int walt_ravg_window;
-extern unsigned int walt_disabled;
+extern bool walt_disabled;
 #endif
 
 /*

kernel/sched/sched.h

@@ -1560,7 +1560,7 @@ static inline unsigned long capacity_orig_of(int cpu)
 
 extern unsigned int sysctl_sched_use_walt_cpu_util;
 extern unsigned int walt_ravg_window;
-extern unsigned int walt_disabled;
+extern bool walt_disabled;
 
 /*
  * cpu_util returns the amount of capacity of a CPU that is used by CFS

kernel/sched/walt.c

@@ -41,25 +41,17 @@ static __read_mostly unsigned int walt_io_is_busy = 0;
 
 unsigned int sysctl_sched_walt_init_task_load_pct = 15;
 
-/* 1 -> use PELT based load stats, 0 -> use window-based load stats */
-unsigned int __read_mostly walt_disabled = 0;
+/* true -> use PELT based load stats, false -> use window-based load stats */
+bool __read_mostly walt_disabled = false;
 
-/* Window size (in ns) */
-__read_mostly unsigned int walt_ravg_window = 20000000;
-
-/* Min window size (in ns) = 10ms */
-#ifdef CONFIG_HZ_300
 /*
- * Tick interval becomes to 3333333 due to
- * rounding error when HZ=300.
+ * Window size (in ns). Adjust for the tick size so that the window
+ * rollover occurs just before the tick boundary.
  */
-#define MIN_SCHED_RAVG_WINDOW (3333333 * 6)
-#else
-#define MIN_SCHED_RAVG_WINDOW 10000000
-#endif
-
-/* Max window size (in ns) = 1s */
-#define MAX_SCHED_RAVG_WINDOW 1000000000
+__read_mostly unsigned int walt_ravg_window =
+					    (20000000 / TICK_NSEC) * TICK_NSEC;
+#define MIN_SCHED_RAVG_WINDOW ((10000000 / TICK_NSEC) * TICK_NSEC)
+#define MAX_SCHED_RAVG_WINDOW ((1000000000 / TICK_NSEC) * TICK_NSEC)
 
 static unsigned int sync_cpu;
 static ktime_t ktime_last;
@@ -180,10 +172,28 @@ static int exiting_task(struct task_struct *p)
 
 static int __init set_walt_ravg_window(char *str)
 {
+	unsigned int adj_window;
+	bool no_walt = walt_disabled;
+
 	get_option(&str, &walt_ravg_window);
 
-	walt_disabled = (walt_ravg_window < MIN_SCHED_RAVG_WINDOW ||
-				walt_ravg_window > MAX_SCHED_RAVG_WINDOW);
+	/* Adjust for CONFIG_HZ */
+	adj_window = (walt_ravg_window / TICK_NSEC) * TICK_NSEC;
+
+	/* Warn if we're a bit too far away from the expected window size */
+	WARN(adj_window < walt_ravg_window - NSEC_PER_MSEC,
+	     "tick-adjusted window size %u, original was %u\n", adj_window,
+	     walt_ravg_window);
+
+	walt_ravg_window = adj_window;
+
+	walt_disabled = walt_disabled ||
+			(walt_ravg_window < MIN_SCHED_RAVG_WINDOW ||
+			 walt_ravg_window > MAX_SCHED_RAVG_WINDOW);
+
+	WARN(!no_walt && walt_disabled,
+	     "invalid window size, disabling WALT\n");
+
 	return 0;
 }
 

kernel/sched/walt.h

@@ -59,6 +59,6 @@ static inline u64 walt_ktime_clock(void) { return 0; }
 
 #endif /* CONFIG_SCHED_WALT */
 
-extern unsigned int walt_disabled;
+extern bool walt_disabled;
 
 #endif