From ee72ef6e12984db43cdf8a1f0194c9302b33e46c Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Sat, 26 Sep 2009 16:01:53 -0400
Subject: [PATCH] qsbr: Use adaptative wait delay

Use a wait delay based on the last Q.S. duration of the thread we are waiting
for.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---
 urcu-qsbr-static.h | 23 +++++++++++++++++++++++
 urcu-qsbr.c        |  4 +++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/urcu-qsbr-static.h b/urcu-qsbr-static.h
index 9cc5db4..d18fabd 100644
--- a/urcu-qsbr-static.h
+++ b/urcu-qsbr-static.h
@@ -34,6 +34,7 @@
 #include <assert.h>
 #include <limits.h>
 #include <sched.h>
+#include <sys/time.h>
 
 #include <compiler.h>
 #include <arch.h>
@@ -181,6 +182,8 @@ extern unsigned long urcu_gp_ctr;
 struct urcu_reader_status {
 	unsigned long qs_gp;
 	unsigned long gp_waiting;
+	unsigned long qs_time_delta_usec;
+	struct timeval qs_time_last;
 };
 
 extern struct urcu_reader_status __thread urcu_reader_status;
@@ -219,8 +222,17 @@ static inline void _rcu_read_unlock(void)
 static inline void _rcu_quiescent_state(void)
 {
 	long gp_ctr;
+	struct timeval current_time;
 
 	smp_mb();
+	gettimeofday(&current_time, NULL);
+	if (current_time.tv_sec - urcu_reader_status.qs_time_last.tv_sec >= 1)
+		_STORE_SHARED(urcu_reader_status.qs_time_delta_usec, 1000000);
+	else
+		_STORE_SHARED(urcu_reader_status.qs_time_delta_usec,
+		      (unsigned long)current_time.tv_usec
+		      - (unsigned long)urcu_reader_status.qs_time_last.tv_usec);
+	urcu_reader_status.qs_time_last = current_time;
 	/*
 	 * volatile accesses can be reordered by the compiler when put in the
 	 * same expression.
@@ -247,6 +259,17 @@ static inline void _rcu_thread_offline(void)
 
 static inline void _rcu_thread_online(void)
 {
+	struct timeval current_time;
+
+	gettimeofday(&current_time, NULL);
+	if (current_time.tv_sec - urcu_reader_status.qs_time_last.tv_sec >= 1)
+		_STORE_SHARED(urcu_reader_status.qs_time_delta_usec, 1000000);
+	else
+		_STORE_SHARED(urcu_reader_status.qs_time_delta_usec,
+		      (unsigned long)current_time.tv_usec
+		      - (unsigned long)urcu_reader_status.qs_time_last.tv_usec);
+	urcu_reader_status.qs_time_last = current_time;
+	_STORE_SHARED(urcu_reader_status.qs_time_delta_usec, 0);
 	_STORE_SHARED(urcu_reader_status.qs_gp, LOAD_SHARED(urcu_gp_ctr));
 	smp_mb();
 }
diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index c275b66..5f06bfa 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -31,6 +31,7 @@
 #include <string.h>
 #include <errno.h>
 #include <poll.h>
+#include <unistd.h>
 
 #define BUILD_QSBR_LIB
 #include "urcu-qsbr-static.h"
@@ -117,7 +118,8 @@ static void wait_for_quiescent_state(void)
 		index->urcu_reader_status->gp_waiting = 1;
 		while (rcu_gp_ongoing(&index->urcu_reader_status->qs_gp)) {
 			if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
-				sched_yield();	/* ideally sched_yield_to() */
+				/* adapted wait time, in us */
+				usleep(LOAD_SHARED(index->urcu_reader_status->qs_time_delta_usec));
 				wait_loops = 0;
 			} else {
 #ifndef HAS_INCOHERENT_CACHES
-- 
2.34.1