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 d368c6faa19b ("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>
(cherry picked from commit e79f447a9762f68d6ecf8371bcf3e970bceb662a)
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index e3bf0b3..f0517de 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -617,7 +617,7 @@
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
/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 85f6e78..af9418a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1604,7 +1604,7 @@
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
diff --git a/kernel/sched/walt.c b/kernel/sched/walt.c
index fa777bd..343c2c9 100644
--- a/kernel/sched/walt.c
+++ b/kernel/sched/walt.c
@@ -42,25 +42,17 @@
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;
@@ -181,10 +173,28 @@
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;
}
diff --git a/kernel/sched/walt.h b/kernel/sched/walt.h
index f56c4da..de7edac 100644
--- a/kernel/sched/walt.h
+++ b/kernel/sched/walt.h
@@ -59,6 +59,6 @@
#endif /* CONFIG_SCHED_WALT */
-extern unsigned int walt_disabled;
+extern bool walt_disabled;
#endif