From 27325ed5a4f770b681c6847352c547d51dbdeb62 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Tue, 16 Dec 2014 19:43:55 -0700
Subject: [PATCH 1/1] gettime: improve gettimeofday() offload support

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 gettime-thread.c | 11 +++++++++--
 gettime.c        |  4 +---
 gettime.h        | 18 ++++++++++++++++++
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/gettime-thread.c b/gettime-thread.c
index 3d49034a..72cc4d8a 100644
--- a/gettime-thread.c
+++ b/gettime-thread.c
@@ -20,8 +20,15 @@ void fio_gtod_init(void)
 
 static void fio_gtod_update(void)
 {
-	if (fio_tv)
-		gettimeofday(fio_tv, NULL);
+	if (fio_tv) {
+		struct timeval __tv;
+
+		gettimeofday(&__tv, NULL);
+		fio_tv->tv_sec = __tv.tv_sec;
+		write_barrier();
+		fio_tv->tv_usec = __tv.tv_usec;
+		write_barrier();
+	}
 }
 
 static void *gtod_thread_main(void *data)
diff --git a/gettime.c b/gettime.c
index 87abca0f..e2746711 100644
--- a/gettime.c
+++ b/gettime.c
@@ -207,10 +207,8 @@ void fio_gettime(struct timeval *tp, void fio_unused *caller)
 
 	gtod_log_caller(caller);
 #endif
-	if (fio_unlikely(fio_tv)) {
-		memcpy(tp, fio_tv, sizeof(*tp));
+	if (fio_unlikely(fio_gettime_offload(tp)))
 		return;
-	}
 
 	__fio_gettime(tp);
 }
diff --git a/gettime.h b/gettime.h
index f0ad20c8..f5412286 100644
--- a/gettime.h
+++ b/gettime.h
@@ -1,6 +1,8 @@
 #ifndef FIO_GETTIME_H
 #define FIO_GETTIME_H
 
+#include "arch/arch.h"
+
 /*
  * Clock sources
  */
@@ -20,4 +22,20 @@ extern void fio_local_clock_init(int);
 
 extern struct timeval *fio_tv;
 
+static inline int fio_gettime_offload(struct timeval *tv)
+{
+	size_t last_sec;
+
+	if (!fio_tv)
+		return 0;
+
+	do {
+		read_barrier();
+		last_sec = tv->tv_sec = fio_tv->tv_sec;
+		tv->tv_usec = fio_tv->tv_usec;
+	} while (fio_tv->tv_sec != last_sec);
+
+	return 1;
+}
+
 #endif
-- 
2.25.1