[PATCH v2] cyclic: Add rate limiting in schedule() via CYCLIC_RATELIMIT_US

[Stefan Roese]

This patch adds the new Kconfig option CONFIG_CYCLIC_RATELIMIT_US which
defines the min allowed time after with a new call into the cyclic
infrastructure is allowed. This results in a rate limiting of the all
functions hooked into the cyclic interface. As it's been noticed that on
some platforms, that high frequent calls to schedule() (replaced from
WATCHDOG_RESET) may lead to a performance degradation.

When a high frequent calling into schedule() is detected, a warning is
logged only once to help indentify this frantic caller.

Signed-off-by: Stefan Roese <sr at denx.de>
Cc: Simon Glass <sjg at chromium.org>
Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
---
- Some spelling fixes (Simon)
- Minor coding style improvement in comment (Simon)

 common/Kconfig                    | 11 +++++++++++
 common/cyclic.c                   | 27 +++++++++++++++++++++++++--
 include/asm-generic/global_data.h |  1 +
 3 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/common/Kconfig b/common/Kconfig
index 973482f07566..7a94883f312f 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -601,6 +601,17 @@ config CYCLIC_MAX_CPU_TIME_US
 	  takes longer than this duration this function will get unregistered
 	  automatically.
 
+config CYCLIC_RATELIMIT_US
+	int "Sets the min time/delay in us after a new call into schedule is done"
+	default 100
+	help
+	  The min allowed time after with a new call into the cyclic
+	  infrastructure is allowed. This results in a rate limiting of the
+	  all functions hooked into the cyclic interface.
+	  As it's been noticed that on some platforms, that high frequent
+	  calls to schedule() (replaced from WATCHDOG_RESET) may lead to a
+	  performance degradation.
+
 endif # CYCLIC
 
 config EVENT
diff --git a/common/cyclic.c b/common/cyclic.c
index a49bfc88f5c0..9b85afc3c095 100644
--- a/common/cyclic.c
+++ b/common/cyclic.c
@@ -12,6 +12,7 @@
 #include <log.h>
 #include <malloc.h>
 #include <time.h>
+#include <linux/bug.h>
 #include <linux/errno.h>
 #include <linux/list.h>
 #include <asm/global_data.h>
@@ -109,8 +110,30 @@ void schedule(void)
 	 * schedule() might get called very early before the cyclic IF is
 	 * ready. Make sure to only call cyclic_run() when it's initalized.
 	 */
-	if (gd)
-		cyclic_run();
+	if (gd) {
+		uint64_t now;
+
+		/*
+		 * Add some rate limiting to not call into the cyclic IF too
+		 * ofter. As it's been noticed that on some platforms, that
+		 * high frequent calls to schedule() (replaced from
+		 * WATCHDOG_RESET) may lead to a performance degradation.
+		 * -> Do not reset the watchdog too often
+		 */
+		now = timer_get_us();
+		if (time_after_eq64(now, gd->cyclic_next_call)) {
+			cyclic_run();
+			gd->cyclic_next_call = now + CONFIG_CYCLIC_RATELIMIT_US;
+		} else {
+			/*
+			 * Throw a warning (only once) to help identifying
+			 * frantic callers
+			 */
+			WARN_ONCE(1, "schedule() called very often, now = %lld us next call at %lld us, dt = %lld us\n",
+				  now, gd->cyclic_next_call,
+				  gd->cyclic_next_call - now);
+		}
+	}
 }
 
 int cyclic_unregister_all(void)
diff --git a/include/asm-generic/global_data.h b/include/asm-generic/global_data.h
index 8fc205ded1a3..0988403d142c 100644
--- a/include/asm-generic/global_data.h
+++ b/include/asm-generic/global_data.h
@@ -490,6 +490,7 @@ struct global_data {
 	 * @cyclic_list: list of registered cyclic functions
 	 */
 	struct hlist_head cyclic_list;
+	uint64_t cyclic_next_call;
 #endif
 	/**
 	 * @dmtag_list: List of DM tags
-- 
2.39.2