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Subject[patch] enable uptime display > 497 days on 32 bit
Dear Linus,

To further lobby this patch and to aid audit of "obvious correctness", I
have split the previous version and sorted the chunks in some logical
order.
Short description follows, while the option for debugging jiffies wraps
is ripped out and sent as a separate mail.

This patch makes 32 bit boxes export correct uptime to userland after
jiffies wraparound. Since uptime is reported in seconds, no userland
application changes are needed.

The patch introduces a get_jiffies64() function that internally counts
jiffies wraps. This way there is no overhead neither in the timer
interrupt nor in functions not interested in a 64bit jiffies value.
A timer is used to detect wraps during long periods without
get_jiffies64() calls.

I also extended the start_time field of struct task_struct to 64 bits
so that ps output will still be ok after the 32 bit wraparound while
keeping sub-second resolution of runtimes.

Idle time overflow is dealt with in the same way, and some uses of 64 bit
jiffies for accounting and the oom killer are included.

Tim


--- linux-2.4.15-pre8/include/linux/sched.h Wed Nov 21 17:49:19 2001
+++ linux-2.4.15-pre8-jiffies64/include/linux/sched.h Wed Nov 21 18:23:18 2001
@@ -351,7 +351,7 @@
unsigned long it_real_incr, it_prof_incr, it_virt_incr;
struct timer_list real_timer;
struct tms times;
- unsigned long start_time;
+ u64 start_time;
long per_cpu_utime[NR_CPUS], per_cpu_stime[NR_CPUS];
/* mm fault and swap info: this can arguably be seen as either mm-specific or thread-specific */
unsigned long min_flt, maj_flt, nswap, cmin_flt, cmaj_flt, cnswap;
@@ -548,6 +548,18 @@
#include <asm/current.h>

extern unsigned long volatile jiffies;
+#if BITS_PER_LONG < 48
+# define NEEDS_JIFFIES64
+ extern u64 get_jiffies64(void);
+#else
+ /* jiffies is wide enough to not wrap for 8716 years at HZ==1024 */
+ static inline u64 get_jiffies64(void)
+ {
+ return (u64)jiffies;
+ }
+#endif
+
+
extern unsigned long itimer_ticks;
extern unsigned long itimer_next;
extern struct timeval xtime;

--- linux-2.4.15-pre8/kernel/timer.c Mon Oct 8 19:41:41 2001
+++ linux-2.4.15-pre8-jiffies64/kernel/timer.c Wed Nov 21 18:19:01 2001
@@ -103,6 +103,8 @@

#define NOOF_TVECS (sizeof(tvecs) / sizeof(tvecs[0]))

+static inline void init_jiffieswrap_timer(void);
+
void init_timervecs (void)
{
int i;
@@ -115,6 +117,8 @@
}
for (i = 0; i < TVR_SIZE; i++)
INIT_LIST_HEAD(tv1.vec + i);
+
+ init_jiffieswrap_timer();
}

static unsigned long timer_jiffies;
@@ -683,6 +687,54 @@
if (TQ_ACTIVE(tq_timer))
mark_bh(TQUEUE_BH);
}
+
+
+#ifdef NEEDS_JIFFIES64
+
+u64 get_jiffies64(void)
+{
+ static unsigned long jiffies_hi = 0;
+ static unsigned long jiffies_last;
+ static spinlock_t jiffies64_lock = SPIN_LOCK_UNLOCKED;
+ unsigned long jiffies_tmp, flags;
+
+ spin_lock_irqsave(&jiffies64_lock, flags);
+ jiffies_tmp = jiffies; /* avoid races */
+ if (jiffies_tmp < jiffies_last) /* We have a wrap */
+ jiffies_hi++;
+ jiffies_last = jiffies_tmp;
+ spin_unlock_irqrestore(&jiffies64_lock, flags);
+
+ return (jiffies_tmp | ((u64)jiffies_hi) << BITS_PER_LONG);
+}
+
+/* use a timer to periodically check for jiffies overflow */
+
+static struct timer_list jiffieswrap_timer;
+#define CHECK_JIFFIESWRAP_INTERVAL (1ul << (BITS_PER_LONG-2))
+
+static void check_jiffieswrap(unsigned long data)
+{
+ mod_timer(&jiffieswrap_timer, jiffies + CHECK_JIFFIESWRAP_INTERVAL);
+ get_jiffies64();
+}
+
+static inline void init_jiffieswrap_timer(void)
+{
+ init_timer(&jiffieswrap_timer);
+ jiffieswrap_timer.expires = jiffies + CHECK_JIFFIESWRAP_INTERVAL;
+ jiffieswrap_timer.function = check_jiffieswrap;
+ add_timer(&jiffieswrap_timer);
+}
+
+#else
+
+static inline void init_jiffieswrap_timer(void)
+{
+}
+
+#endif /* NEEDS_JIFFIES64 */
+

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

--- linux-2.4.15-pre8/kernel/fork.c Wed Oct 24 02:44:15 2001
+++ linux-2.4.15-pre8-jiffies64/kernel/fork.c Wed Nov 21 18:19:01 2001
@@ -647,7 +647,7 @@
}
#endif
p->lock_depth = -1; /* -1 = no lock */
- p->start_time = jiffies;
+ p->start_time = get_jiffies64();

INIT_LIST_HEAD(&p->local_pages);


--- linux-2.4.15-pre8/kernel/info.c Sat Apr 21 01:15:40 2001
+++ linux-2.4.15-pre8-jiffies64/kernel/info.c Wed Nov 21 18:19:01 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();
+ 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-2.4.15-pre8/fs/proc/array.c Thu Oct 11 18:00:01 2001
+++ linux-2.4.15-pre8-jiffies64/fs/proc/array.c Wed Nov 21 18:19:01 2001
@@ -343,7 +343,7 @@
ppid = task->pid ? task->p_opptr->pid : 0;
read_unlock(&tasklist_lock);
res = sprintf(buffer,"%d (%s) %c %d %d %d %d %d %lu %lu \
-%lu %lu %lu %lu %lu %ld %ld %ld %ld %ld %ld %lu %lu %ld %lu %lu %lu %lu %lu \
+%lu %lu %lu %lu %lu %ld %ld %ld %ld %ld %ld %llu %lu %ld %lu %lu %lu %lu %lu \
%lu %lu %lu %lu %lu %lu %lu %lu %d %d\n",
task->pid,
task->comm,
@@ -366,7 +366,7 @@
nice,
0UL /* removed */,
task->it_real_value,
- task->start_time,
+ (unsigned long long)(task->start_time),
vsize,
mm ? mm->rss : 0, /* you might want to shift this left 3 */
task->rlim[RLIMIT_RSS].rlim_cur,

--- linux-2.4.15-pre8/fs/proc/proc_misc.c Wed Nov 21 17:49:16 2001
+++ linux-2.4.15-pre8-jiffies64/fs/proc/proc_misc.c Wed Nov 21 18:37:56 2001
@@ -40,6 +40,7 @@
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/io.h>
+#include <asm/div64.h>


#define LOAD_INT(x) ((x) >> FSHIFT)
@@ -93,37 +94,82 @@
return proc_calc_metrics(page, start, off, count, eof, len);
}

+#if BITS_PER_LONG < 48
+
+u64 get_idle64(void)
+{
+ static unsigned long idle_hi, idle_last;
+ static spinlock_t idle64_lock = SPIN_LOCK_UNLOCKED;
+ unsigned long idle, flags;
+
+ spin_lock_irqsave(&idle64_lock, flags);
+ idle = init_tasks[0]->times.tms_utime + init_tasks[0]->times.tms_stime;
+ if (idle < idle_last) /* We have a wrap */
+ idle_hi++;
+ idle_last = idle;
+ spin_unlock_irqrestore(&idle64_lock, flags);
+
+ return (idle | ((u64)idle_hi) << BITS_PER_LONG);
+}
+
+/* use a timer to periodically check for idle time overflow */
+
+static struct timer_list idlewrap_timer;
+#define CHECK_IDLEWRAP_INTERVAL (1ul << (BITS_PER_LONG-2))
+
+static void check_idlewrap(unsigned long data)
+{
+ mod_timer(&idlewrap_timer, jiffies + CHECK_IDLEWRAP_INTERVAL);
+ get_idle64();
+}
+
+static inline void init_idlewrap_timer(void)
+{
+ init_timer(&idlewrap_timer);
+ idlewrap_timer.expires = jiffies + CHECK_IDLEWRAP_INTERVAL;
+ idlewrap_timer.function = check_idlewrap;
+ add_timer(&idlewrap_timer);
+}
+
+#else
+ /* Idle time won't overflow for 8716 years at HZ==1024 */
+
+static inline u64 get_idle64(void)
+{
+ return (u64)(init_tasks[0]->times.tms_utime
+ + init_tasks[0]->times.tms_stime);
+}
+
+static inline void init_jiffieswrap_timer(void)
+{
+}
+
+#endif /* BITS_PER_LONG < 48 */
+
static int uptime_read_proc(char *page, char **start, off_t off,
int count, int *eof, void *data)
{
- unsigned long uptime;
- unsigned long idle;
+ u64 uptime, idle;
+ unsigned long uptime_remainder, idle_remainder;
int len;

- uptime = jiffies;
- idle = init_tasks[0]->times.tms_utime + init_tasks[0]->times.tms_stime;
+ uptime = get_jiffies64();
+ uptime_remainder = (unsigned long) do_div(uptime, HZ);
+ idle = get_idle64();
+ idle_remainder = (unsigned long) do_div(idle, HZ);

- /* The formula for the fraction parts 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
- in the above formulas are truncating. For HZ being a power of 10, the
- calculations simplify to the version in the #else part (if the printf
- format is adapted to the same number of digits as zeroes in HZ.
- */
#if HZ!=100
len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
- uptime / HZ,
- (((uptime % HZ) * 100) / HZ) % 100,
- idle / HZ,
- (((idle % HZ) * 100) / HZ) % 100);
+ (unsigned long) uptime,
+ (uptime_remainder * 100) / HZ,
+ (unsigned long) idle,
+ (idle_remainder * 100) / HZ);
#else
len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
- uptime / HZ,
- uptime % HZ,
- idle / HZ,
- idle % HZ);
+ (unsigned long) uptime,
+ uptime_remainder,
+ (unsigned long) idle,
+ idle_remainder);
#endif
return proc_calc_metrics(page, start, off, count, eof, len);
}
@@ -565,4 +611,6 @@
slabinfo_read_proc, NULL);
if (entry)
entry->write_proc = slabinfo_write_proc;
+
+ init_idlewrap_timer();
}

--- linux-2.4.15-pre8-jiffies64-2/mm/oom_kill.c Sun Nov 4 02:05:25 2001
+++ linux-2.4.15-pre8-jiffies64/mm/oom_kill.c Wed Nov 21 18:19:01 2001
@@ -69,11 +69,10 @@
/*
* CPU time is in seconds and run time is in minutes. There is no
* particular reason for this other than that it turned out to work
- * very well in practice. This is not safe against jiffie wraps
- * but we don't care _that_ much...
+ * very well in practice.
*/
cpu_time = (p->times.tms_utime + p->times.tms_stime) >> (SHIFT_HZ + 3);
- run_time = (jiffies - p->start_time) >> (SHIFT_HZ + 10);
+ run_time = (get_jiffies64() - p->start_time) >> (SHIFT_HZ + 10);

points /= int_sqrt(cpu_time);
points /= int_sqrt(int_sqrt(run_time));
--- linux-2.4.15-pre8/kernel/acct.c Mon Mar 19 21:35:08 2001
+++ linux-2.4.15-pre8-jiffies64/kernel/acct.c Wed Nov 21 18:19:01 2001
@@ -56,6 +56,7 @@
#include <linux/tty.h>

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

/*
* These constants control the amount of freespace that suspend and
@@ -227,20 +228,24 @@
* This routine has been adopted from the encode_comp_t() function in
* the kern_acct.c file of the FreeBSD operating system. The encoding
* is a 13-bit fraction with a 3-bit (base 8) exponent.
+ *
+ * Bumped up to encode 64 bit values. Unfortunately the result may
+ * overflow now.
*/

#define MANTSIZE 13 /* 13 bit mantissa. */
-#define EXPSIZE 3 /* Base 8 (3 bit) exponent. */
+#define EXPSIZE 3 /* 3 bit exponent. */
+#define EXPBASE 3 /* Base 8 (3 bit) exponent. */
#define MAXFRACT ((1 << MANTSIZE) - 1) /* Maximum fractional value. */

-static comp_t encode_comp_t(unsigned long value)
+static comp_t encode_comp_t(u64 value)
{
int exp, rnd;

exp = rnd = 0;
while (value > MAXFRACT) {
- rnd = value & (1 << (EXPSIZE - 1)); /* Round up? */
- value >>= EXPSIZE; /* Base 8 exponent == 3 bit shift. */
+ rnd = value & (1 << (EXPBASE - 1)); /* Round up? */
+ value >>= EXPBASE; /* Base 8 exponent == 3 bit shift. */
exp++;
}

@@ -248,16 +253,21 @@
* If we need to round up, do it (and handle overflow correctly).
*/
if (rnd && (++value > MAXFRACT)) {
- value >>= EXPSIZE;
+ value >>= EXPBASE;
exp++;
}

/*
* Clean it up and polish it off.
*/
- exp <<= MANTSIZE; /* Shift the exponent into place */
- exp += value; /* and add on the mantissa. */
- return exp;
+ if (exp >= (1 << EXPSIZE)) {
+ /* Overflow. Return largest representable number instead. */
+ return (1ul << (MANTSIZE + EXPSIZE)) - 1;
+ } else {
+ exp <<= MANTSIZE; /* Shift the exponent into place */
+ exp += value; /* and add on the mantissa. */
+ return exp;
+ }
}

/*
@@ -277,6 +287,7 @@
struct acct ac;
mm_segment_t fs;
unsigned long vsize;
+ u64 elapsed;

/*
* First check to see if there is enough free_space to continue
@@ -294,8 +305,10 @@
strncpy(ac.ac_comm, current->comm, ACCT_COMM);
ac.ac_comm[ACCT_COMM - 1] = '\0';

- ac.ac_btime = CT_TO_SECS(current->start_time) + (xtime.tv_sec - (jiffies / HZ));
- ac.ac_etime = encode_comp_t(jiffies - current->start_time);
+ elapsed = get_jiffies64() - current->start_time;
+ ac.ac_etime = encode_comp_t(elapsed);
+ do_div(elapsed, HZ);
+ ac.ac_btime = xtime.tv_sec - elapsed;
ac.ac_utime = encode_comp_t(current->times.tms_utime);
ac.ac_stime = encode_comp_t(current->times.tms_stime);
ac.ac_uid = current->uid;
-
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