taskstats: use real microsecond granularity for CPU times

The taskstats interface uses microsecond granularity for the user and
system time values. The conversion from cputime to the taskstats values
uses the cputime_to_msecs primitive which effectively limits the
granularity to milliseconds. Add the cputime_to_usecs primitive for
architectures that have better, more precise CPU time values. Remove
cputime_to_msecs primitive because there are no more users left.

Signed-off-by: Michael Holzheu <[e-mail]>
Acked-by: Balbir Singh <[e-mail]>
Cc: Luck Tony <[e-mail]>
Cc: Shailabh Nagar <[e-mail]>
Cc: Martin Schwidefsky <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Shailabh Nagar <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/ia64/include/asm/cputime.h

···
 #define jiffies64_to_cputime64(__jif)	((__jif) * (NSEC_PER_SEC / HZ))
 
 /*
- * Convert cputime <-> milliseconds
+ * Convert cputime <-> microseconds
  */
-#define cputime_to_msecs(__ct)		((__ct) / NSEC_PER_MSEC)
-#define msecs_to_cputime(__msecs)	((__msecs) * NSEC_PER_MSEC)
+#define cputime_to_usecs(__ct)		((__ct) / NSEC_PER_USEC)
+#define usecs_to_cputime(__usecs)	((__usecs) * NSEC_PER_USEC)
 
 /*
  * Convert cputime <-> seconds

arch/powerpc/include/asm/cputime.h

···
 }
 
 /*
- * Convert cputime <-> milliseconds
+ * Convert cputime <-> microseconds
  */
 extern u64 __cputime_msec_factor;
 
-static inline unsigned long cputime_to_msecs(const cputime_t ct)
+static inline unsigned long cputime_to_usecs(const cputime_t ct)
 {
-	return mulhdu(ct, __cputime_msec_factor);
+	return mulhdu(ct, __cputime_msec_factor) * USEC_PER_MSEC;
 }
 
-static inline cputime_t msecs_to_cputime(const unsigned long ms)
+static inline cputime_t usecs_to_cputime(const unsigned long us)
 {
 	cputime_t ct;
 	unsigned long sec;
 
 	/* have to be a little careful about overflow */
-	ct = ms % 1000;
-	sec = ms / 1000;
+	ct = us % 1000000;
+	sec = us / 1000000;
 	if (ct) {
 		ct *= tb_ticks_per_sec;
 		do_div(ct, 1000);

arch/s390/include/asm/cputime.h

···
 }
 
 /*
- * Convert cputime to milliseconds and back.
+ * Convert cputime to microseconds and back.
  */
 static inline unsigned int
-cputime_to_msecs(const cputime_t cputime)
+cputime_to_usecs(const cputime_t cputime)
 {
-	return cputime_div(cputime, 4096000);
+	return cputime_div(cputime, 4096);
 }
 
 static inline cputime_t
-msecs_to_cputime(const unsigned int m)
+usecs_to_cputime(const unsigned int m)
 {
-	return (cputime_t) m * 4096000;
+	return (cputime_t) m * 4096;
 }
 
 /*

include/asm-generic/cputime.h

···
 
 
 /*
- * Convert cputime to milliseconds and back.
+ * Convert cputime to microseconds and back.
  */
-#define cputime_to_msecs(__ct)		jiffies_to_msecs(__ct)
-#define msecs_to_cputime(__msecs)	msecs_to_jiffies(__msecs)
+#define cputime_to_usecs(__ct)		jiffies_to_usecs(__ct);
+#define usecs_to_cputime(__msecs)	usecs_to_jiffies(__msecs);
 
 /*
  * Convert cputime to seconds and back.

kernel/tsacct.c

···
 	stats->ac_ppid	 = pid_alive(tsk) ?
 				rcu_dereference(tsk->real_parent)->tgid : 0;
 	rcu_read_unlock();
-	stats->ac_utime	 = cputime_to_msecs(tsk->utime) * USEC_PER_MSEC;
-	stats->ac_stime	 = cputime_to_msecs(tsk->stime) * USEC_PER_MSEC;
-	stats->ac_utimescaled =
-		cputime_to_msecs(tsk->utimescaled) * USEC_PER_MSEC;
-	stats->ac_stimescaled =
-		cputime_to_msecs(tsk->stimescaled) * USEC_PER_MSEC;
+	stats->ac_utime = cputime_to_usecs(tsk->utime);
+	stats->ac_stime = cputime_to_usecs(tsk->stime);
+	stats->ac_utimescaled = cputime_to_usecs(tsk->utimescaled);
+	stats->ac_stimescaled = cputime_to_usecs(tsk->stimescaled);
 	stats->ac_minflt = tsk->min_flt;
 	stats->ac_majflt = tsk->maj_flt;