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Subject[patch][rfc] enable uptime display > 497 days on 32 bit
This is a polished version of the patch that came out of the
"[Patch] Re: Nasty suprise with uptime" thread last november.

It makes the kernel export correct uptimes after jiffies wraparound
(497 days after boot with HZ=100 on 32 bit, somewhat sooner with HZ=1024)
and keeps ps output after wrap sane as well. No userland application
changes are needed.
The performance hit is minimal as the upper 32bit of the jiffies counter
are only updated when they are actually used (the get_jiffies64() routine
is introduced for this). A timer is used to check at least once between
two wraps, since timers are implemented very efficiently. 64 bit idle
time is done in the same way.

Before submitting the patch to Marcelo for 2.4.19-pre, I'd like to get
some comments, especially on the following points:

1. Does the patch, in particular the introduction of get_jiffies64(),
interfere with the high-res-timers project
(http://sourceforge.net/projects/high-res-timers) in any bad way?

2. I bumped up the start_time field of struct task_struct from 32 to
64 bits when borrowing just some extra bits would suffice.
Any suggestions, where these could be stolen, and whether this
micro-optimization is worth the trouble?

3. Maybe accounting is not worth being touched at all. comp_t is able
to hold values up to a little less that 2^34, so I stuffed the
elapsed time into that. CPU times however, although probably a
little less than real times, will still overflow if >= 2^32 secs.

User space accounting programs using 32bit integers will overflow
anyways and see the same values as without the patch.

Some people wondered why this not yet went into mainline.
Well, previous kernels sometimes locked up solidly at jiffies wraparound,
and I didn't want to imply a false feeling of safety by just fixing the
exported uptime.
As quite a few fixes in this area went into 2.4.18 (with some more to come
soon), this should not hinder inclusion anymore.
A patch for setting the jiffies counter to a pre-wrap value should
find the remaining glitches, it will follow in a separate mail.

Tim


--- linux-2.4.19-pre1/include/linux/sched.h Fri Dec 21 18:42:03 2001
+++ linux-2.4.19-pre1-j64/include/linux/sched.h Tue Feb 26 16:44:08 2002
@@ -359,7 +359,7 @@
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;
@@ -571,6 +571,18 @@
#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-2.4.19-pre1/kernel/timer.c Mon Oct 8 19:41:41 2001
+++ linux-2.4.19-pre1-j64/kernel/timer.c Tue Feb 26 16:13:35 2002
@@ -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 +687,53 @@
if (TQ_ACTIVE(tq_timer))
mark_bh(TQUEUE_BH);
}
+
+
+#ifdef NEEDS_JIFFIES64
+
+u64 get_jiffies64(void)
+{
+ static unsigned long jiffies_hi, 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-2.4.19-pre1/kernel/fork.c Sun Feb 24 19:20:43 2002
+++ linux-2.4.19-pre1-j64/kernel/fork.c Tue Feb 26 16:13:35 2002
@@ -657,7 +657,7 @@
}
#endif
p->lock_depth = -1; /* -1 = no lock */
- p->start_time = jiffies;
+ p->start_time = get_jiffies64();

INIT_LIST_HEAD(&p->local_pages);

--- linux-2.4.19-pre1/kernel/info.c Sat Apr 21 01:15:40 2001
+++ linux-2.4.19-pre1-j64/kernel/info.c Tue Feb 26 16:13:35 2002
@@ -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-2.4.19-pre1/fs/proc/array.c Thu Oct 11 18:00:01 2001
+++ linux-2.4.19-pre1-j64/fs/proc/array.c Tue Feb 26 16:13:35 2002
@@ -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-2.4.19-pre1/fs/proc/proc_misc.c Wed Nov 21 06:29:09 2001
+++ linux-2.4.19-pre1-j64/fs/proc/proc_misc.c Tue Feb 26 16:50:45 2002
@@ -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);
}
@@ -240,7 +286,7 @@
{
int i, len;
extern unsigned long total_forks;
- unsigned long jif = jiffies;
+ u64 jif = get_jiffies64();
unsigned int sum = 0, user = 0, nice = 0, system = 0;
int major, disk;

@@ -256,17 +302,19 @@
#endif
}

- len = sprintf(page, "cpu %u %u %u %lu\n", user, nice, system,
- jif * smp_num_cpus - (user + nice + system));
+ len = sprintf(page, "cpu %u %u %u %llu\n", user, nice, system,
+ (unsigned long long) jif * smp_num_cpus
+ - user - nice - system);
for (i = 0 ; i < smp_num_cpus; i++)
- len += sprintf(page + len, "cpu%d %u %u %u %lu\n",
+ len += sprintf(page + len, "cpu%d %u %u %u %llu\n",
i,
kstat.per_cpu_user[cpu_logical_map(i)],
kstat.per_cpu_nice[cpu_logical_map(i)],
kstat.per_cpu_system[cpu_logical_map(i)],
- jif - ( kstat.per_cpu_user[cpu_logical_map(i)] \
- + kstat.per_cpu_nice[cpu_logical_map(i)] \
- + kstat.per_cpu_system[cpu_logical_map(i)]));
+ (unsigned long long) jif
+ - kstat.per_cpu_user[cpu_logical_map(i)]
+ - kstat.per_cpu_nice[cpu_logical_map(i)]
+ - kstat.per_cpu_system[cpu_logical_map(i)]);
len += sprintf(page + len,
"page %u %u\n"
"swap %u %u\n"
@@ -302,12 +350,13 @@
}
}

+ do_div(jif, HZ);
len += sprintf(page + len,
"\nctxt %u\n"
"btime %lu\n"
"processes %lu\n",
kstat.context_swtch,
- xtime.tv_sec - jif / HZ,
+ xtime.tv_sec - (unsigned long) jif,
total_forks);

return proc_calc_metrics(page, start, off, count, eof, len);
@@ -565,4 +614,6 @@
slabinfo_read_proc, NULL);
if (entry)
entry->write_proc = slabinfo_write_proc;
+
+ init_idlewrap_timer();
}
--- linux-2.4.19-pre1/mm/oom_kill.c Sun Nov 4 02:05:25 2001
+++ linux-2.4.19-pre1-j64/mm/oom_kill.c Tue Feb 26 16:13:35 2002
@@ -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-2.4.19-pre1/kernel/acct.c Mon Mar 19 21:35:08 2001
+++ linux-2.4.19-pre1-j64/kernel/acct.c Tue Feb 26 16:13:35 2002
@@ -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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