From: Jens Axboe <jens.axboe@oracle.com>
Date: Thu, 13 Nov 2008 11:07:20 +0000 (+0100)
Subject: Fix backwards clock on tsc source with Linux
X-Git-Tag: fio-1.23~4
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=3e4889209b86409283d1e87bb6b5c9980495c2c6;p=fio.git

Fix backwards clock on tsc source with Linux

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---

diff --git a/gettime.c b/gettime.c
index 2753faec..80eeaf14 100644
--- a/gettime.c
+++ b/gettime.c
@@ -10,6 +10,8 @@
 #include "hash.h"
 
 static int clock_gettime_works;
+static struct timeval last_tv;
+static int last_tv_valid;
 
 #ifdef FIO_DEBUG_TIME
 
@@ -128,4 +130,18 @@ gtod:
 		tp->tv_sec = ts.tv_sec;
 		tp->tv_usec = ts.tv_nsec / 1000;
 	}
+
+	/*
+	 * If Linux is using the tsc clock on non-synced processors,
+	 * sometimes time can appear to drift backwards. Fix that up.
+	 */
+	if (last_tv_valid) {
+		if (tp->tv_sec < last_tv.tv_sec)
+			tp->tv_sec = last_tv.tv_sec;
+		else if (last_tv.tv_sec == tp->tv_sec &&
+			 tp->tv_usec < last_tv.tv_usec)
+			tp->tv_usec = last_tv.tv_usec;
+	}
+	last_tv_valid = 1;
+	memcpy(&last_tv, tp, sizeof(*tp));
 }