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Date: Tue, 25 Nov 2003 11:42:38 -0500
From: Joe Korty <joe.korty@ccur.com>
To: Peter Chubb <peter@chubb.wattle.id.au>
Cc: root@chaos.analogic.com, George Anzinger <george@mvista.com>,
       Stephen Hemminger <shemminger@osdl.org>,
       Gabriel Paubert <paubert@iram.es>, john stultz <johnstul@us.ibm.com>,
       Linus Torvalds <torvalds@osdl.org>, lkml <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>
Subject: [RFC] possible erronous use of tick_usec in do_gettimeofday
Message-ID: <20031125164237.GA15498@rudolph.ccur.com>
Reply-To: Joe Korty <joe.korty@ccur.com>
References: <1067300966.1118.378.camel@cog.beaverton.ibm.com> <20031027171738.1f962565.shemminger@osdl.org> <20031028115558.GA20482@iram.es> <20031028102120.01987aa4.shemminger@osdl.org> <20031029100745.GA6674@iram.es> <20031029113850.047282c4.shemminger@osdl.org> <16288.17470.778408.883304@wombat.chubb.wattle.id.au> <3FA1838C.3060909@mvista.com> <Pine.LNX.4.53.0310301645170.16005@chaos> <16289.39801.239846.9369@wombat.chubb.wattle.id.au>
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test10's version of do_gettimeofday is using tick_usec which is
defined in terms of USER_HZ not HZ.

Against 2.6.0-test10-bk1.  Compiled, not tested, for comment only.

Joe

--- base/arch/i386/kernel/time.c	2003-11-23 20:31:55.000000000 -0500
+++ new/arch/i386/kernel/time.c	2003-11-25 11:22:38.000000000 -0500
@@ -94,7 +94,7 @@
 {
 	unsigned long seq;
 	unsigned long usec, sec;
-	unsigned long max_ntp_tick = tick_usec - tickadj;
+	unsigned long max_ntp_tick;
 
 	do {
 		unsigned long lost;
@@ -110,13 +110,14 @@
 		 * Better to lose some accuracy than have time go backwards..
 		 */
 		if (unlikely(time_adjust < 0)) {
+			max_ntp_tick = (USEC_PER_SEC / HZ) - tickadj;
 			usec = min(usec, max_ntp_tick);
 
 			if (lost)
 				usec += lost * max_ntp_tick;
 		}
 		else if (unlikely(lost))
-			usec += lost * tick_usec;
+			usec += lost * (USEC_PER_SEC / HZ);
 
 		sec = xtime.tv_sec;
 		usec += (xtime.tv_nsec / 1000);