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Date: Thu, 1 Nov 2001 01:52:26 +0100 (CET)
From: Tim Schmielau <tim@physik3.uni-rostock.de>
To: Andreas Dilger <adilger@turbolabs.com>
cc: <linux-kernel@vger.kernel.org>, J Sloan <jjs@lexus.com>
Subject: Re: [Patch] Re: Nasty suprise with uptime
In-Reply-To: <Pine.LNX.4.30.0111010107200.31315-100000@gans.physik3.uni-rostock.de>
Message-ID: <Pine.LNX.4.30.0111010144570.31417-100000@gans.physik3.uni-rostock.de>
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On Thu, 1 Nov 2001, Tim Schmielau wrote:

> On Wed, 31 Oct 2001, Andreas Dilger wrote:
>
> > > +u64 get_jiffies64(void)
> > > +{
> > > +	static unsigned long jiffies_hi = 0;
> > > +	static unsigned long jiffies_last = INITIAL_JIFFIES;
> > > +	static unsigned long jiffies_tmp;
> >         ^^^^^^ jiffies_tmp doesn't need to be static.
>
> Yes, cut and paste error, sorry. And I wanted this patch to be final for
> today...
>


OK, absolutely last patch for today. Sorry to bother everyone, but the
jiffies wraparound logic was broken in the previous patch.

As stated before, I would kindly ask for widespread testing PROVIDED IT IS
OK FOR YOU TO RISK THE STABILITY OF YOUR BOX!


Tim


--- linux-2.4.14-pre6/fs/proc/proc_misc.c	Thu Oct 11 19:46:57 2001
+++ linux-2.4.14-pre6-jiffies64/fs/proc/proc_misc.c	Wed Oct 31 22:53:55 2001
@@ -39,6 +39,7 @@
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
 #include <asm/io.h>
+#include <asm/div64.h>


 #define LOAD_INT(x) ((x) >> FSHIFT)
@@ -103,15 +104,19 @@
 static int uptime_read_proc(char *page, char **start, off_t off,
 				 int count, int *eof, void *data)
 {
-	unsigned long uptime;
+	u64 uptime;
+	unsigned long remainder;
 	unsigned long idle;
 	int len;

-	uptime = jiffies;
+	uptime = get_jiffies64() - INITIAL_JIFFIES;
+	remainder = (unsigned long) do_div(uptime, HZ);
+
 	idle = init_tasks[0]->times.tms_utime + init_tasks[0]->times.tms_stime;

-	/* The formula for the fraction parts really is ((t * 100) / HZ) % 100, but
-	   that would overflow about every five days at HZ == 100.
+	/* The formula for the fraction part of the idle time really is
+	   ((t * 100) / HZ) % 100, but that would overflow about
+	    every five days at HZ == 100.
 	   Therefore the identity a = (a / b) * b + a % b is used so that it is
 	   calculated as (((t / HZ) * 100) + ((t % HZ) * 100) / HZ) % 100.
 	   The part in front of the '+' always evaluates as 0 (mod 100). All divisions
@@ -121,14 +126,14 @@
 	 */
 #if HZ!=100
 	len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
-		uptime / HZ,
-		(((uptime % HZ) * 100) / HZ) % 100,
+		(unsigned long) uptime,
+		(remainder * 100) / HZ,
 		idle / HZ,
 		(((idle % HZ) * 100) / HZ) % 100);
 #else
 	len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
-		uptime / HZ,
-		uptime % HZ,
+		(unsigned long) uptime,
+		remainder,
 		idle / HZ,
 		idle % HZ);
 #endif
--- linux-2.4.14-pre6/kernel/timer.c	Mon Oct  8 19:41:41 2001
+++ linux-2.4.14-pre6-jiffies64/kernel/timer.c	Thu Nov  1 01:37:12 2001
@@ -65,7 +65,7 @@

 extern int do_setitimer(int, struct itimerval *, struct itimerval *);

-unsigned long volatile jiffies;
+unsigned long volatile jiffies = INITIAL_JIFFIES;

 unsigned int * prof_buffer;
 unsigned long prof_len;
@@ -117,7 +117,7 @@
 		INIT_LIST_HEAD(tv1.vec + i);
 }

-static unsigned long timer_jiffies;
+static unsigned long timer_jiffies = INITIAL_JIFFIES;

 static inline void internal_add_timer(struct timer_list *timer)
 {
@@ -638,7 +638,7 @@
 }

 /* jiffies at the most recent update of wall time */
-unsigned long wall_jiffies;
+unsigned long wall_jiffies = INITIAL_JIFFIES;

 /*
  * This spinlock protect us from races in SMP while playing with xtime. -arca
@@ -683,6 +683,34 @@
 	if (TQ_ACTIVE(tq_timer))
 		mark_bh(TQUEUE_BH);
 }
+
+
+#if BITS_PER_LONG < 48
+
+u64 get_jiffies64(void)
+{
+	static unsigned long jiffies_hi = 0;
+	static unsigned long jiffies_last = INITIAL_JIFFIES;
+	unsigned long jiffies_tmp;
+
+	jiffies_tmp = jiffies;   /* avoid races */
+	if (jiffies_tmp < jiffies_last)   /* We have a wrap */
+		jiffies_hi++;
+	jiffies_last = jiffies_tmp;
+
+	return (jiffies_tmp | ((u64)jiffies_hi) << BITS_PER_LONG);
+}
+
+#else
+ /* jiffies is wide enough to not wrap for 8716 years at HZ==1024 */
+
+static inline u64 get_jiffies64(void)
+{
+	return (u64)jiffies;
+}
+
+#endif /* BITS_PER_LONG < 48 */
+

 #if !defined(__alpha__) && !defined(__ia64__)

--- linux-2.4.14-pre6/kernel/info.c	Sat Apr 21 01:15:40 2001
+++ linux-2.4.14-pre6-jiffies64/kernel/info.c	Wed Oct 31 23:15:26 2001
@@ -12,15 +12,19 @@
 #include <linux/smp_lock.h>

 #include <asm/uaccess.h>
+#include <asm/div64.h>

 asmlinkage long sys_sysinfo(struct sysinfo *info)
 {
 	struct sysinfo val;
+	u64 uptime;

 	memset((char *)&val, 0, sizeof(struct sysinfo));

 	cli();
-	val.uptime = jiffies / HZ;
+	uptime = get_jiffies64() - INITIAL_JIFFIES;
+	do_div(uptime, HZ);
+	val.uptime = (unsigned long) uptime;

 	val.loads[0] = avenrun[0] << (SI_LOAD_SHIFT - FSHIFT);
 	val.loads[1] = avenrun[1] << (SI_LOAD_SHIFT - FSHIFT);
--- linux-2.4.14-pre6/include/linux/sched.h	Wed Oct 31 23:06:23 2001
+++ linux-2.4.14-pre6-jiffies64/include/linux/sched.h	Wed Oct 31 23:23:51 2001
@@ -543,7 +543,10 @@

 #include <asm/current.h>

+#define INITIAL_JIFFIES 0xFFFFD000ul
 extern unsigned long volatile jiffies;
+extern u64 get_jiffies64(void);
+
 extern unsigned long itimer_ticks;
 extern unsigned long itimer_next;
 extern struct timeval xtime;

-
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