[PATCH] Posix compliant cpu clocks

POSIX clocks are to be implemented in the following way according
to V3 of the Single Unix Specification:

1. CLOCK_PROCESS_CPUTIME_ID

  Implementations shall also support the special clockid_t value
  CLOCK_PROCESS_CPUTIME_ID, which represents the CPU-time clock of the
  calling process when invoking one of the clock_*() or timer_*()
  functions. For these clock IDs, the values returned by clock_gettime() and
  specified by clock_settime() represent the amount of execution time of the
  process associated with the clock.

2. CLOCK_THREAD_CPUTIME_ID

  Implementations shall also support the special clockid_t value
  CLOCK_THREAD_CPUTIME_ID, which represents the CPU-time clock of the
  calling thread when invoking one of the clock_*() or timer_*()
  functions. For these clock IDs, the values returned by clock_gettime()
  and specified by clock_settime() shall represent the amount of
  execution time of the thread associated with the clock.

These times mentioned are CPU processing times and not the time that has
passed since the startup of a process. Glibc currently provides its own
implementation of these two clocks which is designed to return the time
that passed since the startup of a process or a thread.

Moreover Glibc's clocks are bound to CPU timers which is problematic when the
frequency of the clock changes or the process is moved to a different
processor whose cpu timer may not be fully synchronized to the cpu timer
of the current CPU. This patchset results in a both clocks working reliably.

The patch also implements the access to other the thread and process clocks
of linux processes by using negative clockid's:

1. For CLOCK_PROCESS_CPUTIME_ID: -pid
2. For CLOCK_THREAD_CPUTIME_ID: -(pid + PID_MAX_LIMIT)

This allows

clock_getcpuclockid(pid) to return -pid

and

pthread_getcpuiclock(pid) to return -(pid + PID_MAX_LIMIT)

to allow access to the corresponding clocks.

Todo:
- The timer API to generate events by a non tick based timer is not
  usable in its current state. The posix timer API seems to be only
  useful at this point to define clock_get/set. Need to revise this.
- Implement timed interrupts in mmtimer after API is revised.

The mmtimer patch is unchanged from V6 and stays as is in 2.6.9-rc3-mm2.
But I expect to update the driver as soon as the interface to setup hardware
timer interrupts is usable.

Single Thread Testing
  CLOCK_THREAD_CPUTIME_ID=          0.494140878 resolution= 0.000976563
 CLOCK_PROCESS_CPUTIME_ID=          0.494140878 resolution= 0.000976563
Multi Thread Testing
Starting Thread: 0 1 2 3 4 5 6 7 8 9
 Joining Thread: 0 1 2 3 4 5 6 7 8 9
0 Cycles=      0 Thread=  0.000000000ns Process=  0.495117441ns
1 Cycles=1000000 Thread=  0.140625072ns Process=  2.523438792ns
2 Cycles=2000000 Thread=  0.966797370ns Process=  8.512699671ns
3 Cycles=3000000 Thread=  0.806641038ns Process=  7.561527309ns
4 Cycles=4000000 Thread=  1.865235330ns Process= 12.891608163ns
5 Cycles=5000000 Thread=  1.604493009ns Process= 11.528326215ns
6 Cycles=6000000 Thread=  2.086915131ns Process= 13.500983475ns
7 Cycles=7000000 Thread=  2.245118337ns Process= 13.947272766ns
8 Cycles=8000000 Thread=  1.604493009ns Process= 12.252935961ns
9 Cycles=9000000 Thread=  2.160157356ns Process= 13.977546219ns

Clock status at the end of the timer tests:
          Gettimeofday() = 1097084999.489938000
           CLOCK_REALTIME= 1097084999.490116229 resolution= 0.000000040
          CLOCK_MONOTONIC=        177.071675109 resolution= 0.000000040
 CLOCK_PROCESS_CPUTIME_ID=         13.978522782 resolution= 0.000976563
  CLOCK_THREAD_CPUTIME_ID=          0.497070567 resolution= 0.000976563
          CLOCK_SGI_CYCLE=        229.967982280 resolution= 0.000000040
PROCESS clock of 1 (init)=          4.833986850 resolution= 0.000976563
 THREAD clock of 1 (init)=          0.009765630 resolution= 0.000976563
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/posix-timers.h

@@ -33,9 +33,10 @@ struct k_clock {
 	struct k_clock_abs *abs_struct;
 	int (*clock_set) (struct timespec * tp);
 	int (*clock_get) (struct timespec * tp);
-	int (*nsleep) (int flags,
-		       struct timespec * new_setting,
-		       struct itimerspec * old_setting);
+	int (*timer_create) (int which_clock, struct sigevent __user *timer_event_spec,
+			timer_t __user * created_timer_id);
+	int (*nsleep) (int which_clock, int flags,
+		       struct timespec * t);
 	int (*timer_set) (struct k_itimer * timr, int flags,
 			  struct itimerspec * new_setting,
 			  struct itimerspec * old_setting);
@@ -43,6 +44,17 @@ struct k_clock {
 	void (*timer_get) (struct k_itimer * timr,
 			   struct itimerspec * cur_setting);
 };
+
+void register_posix_clock(int clock_id, struct k_clock *new_clock);
+
+/* Error handlers for timer_create, nanosleep and settime */
+int do_posix_clock_notimer_create(int which_clock,
+                struct sigevent __user *time_event_spec,
+                timer_t __user *created_timer_id);
+
+int do_posix_clock_nonanosleep(int which_clock, int flags, struct timespec * t);
+int do_posix_clock_nosettime(struct timespec *tp);
+
 struct now_struct {
 	unsigned long jiffies;
 };
@@ -62,3 +74,4 @@ struct now_struct {
               }								\
             }while (0)
 #endif
+

include/linux/time.h

@@ -157,7 +157,12 @@ struct	itimerval {
 #define CLOCK_REALTIME_HR	 4
 #define CLOCK_MONOTONIC_HR	  5
 
-#define MAX_CLOCKS 6
+/*
+ * The IDs of various hardware clocks
+ */
+
+
+#define MAX_CLOCKS 16
 #define CLOCKS_MASK  (CLOCK_REALTIME | CLOCK_MONOTONIC | \
                      CLOCK_REALTIME_HR | CLOCK_MONOTONIC_HR)
 #define CLOCKS_MONO (CLOCK_MONOTONIC & CLOCK_MONOTONIC_HR)

kernel/posix-timers.c

@@ -10,6 +10,10 @@
  * 2004-06-01  Fix CLOCK_REALTIME clock/timer TIMER_ABSTIME bug.
  *			     Copyright (C) 2004 Boris Hu
  *
+ * 2004-07-27 Provide POSIX compliant clocks
+ *		CLOCK_PROCESS_CPUTIME_ID and CLOCK_THREAD_CPUTIME_ID.
+ *		by Christoph Lameter
+ *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or (at
@@ -134,18 +138,10 @@ static spinlock_t idr_lock = SPIN_LOCK_UNLOCKED;
  *	    resolution.	 Here we define the standard CLOCK_REALTIME as a
  *	    1/HZ resolution clock.
  *
- * CPUTIME & THREAD_CPUTIME: We are not, at this time, definding these
- *	    two clocks (and the other process related clocks (Std
- *	    1003.1d-1999).  The way these should be supported, we think,
- *	    is to use large negative numbers for the two clocks that are
- *	    pinned to the executing process and to use -pid for clocks
- *	    pinned to particular pids.	Calls which supported these clock
- *	    ids would split early in the function.
- *
  * RESOLUTION: Clock resolution is used to round up timer and interval
  *	    times, NOT to report clock times, which are reported with as
  *	    much resolution as the system can muster.  In some cases this
- *	    resolution may depend on the underlaying clock hardware and
+ *	    resolution may depend on the underlying clock hardware and
  *	    may not be quantifiable until run time, and only then is the
  *	    necessary code is written.	The standard says we should say
  *	    something about this issue in the documentation...
@@ -163,7 +159,7 @@ static spinlock_t idr_lock = SPIN_LOCK_UNLOCKED;
  *
  *          At this time all functions EXCEPT clock_nanosleep can be
  *          redirected by the CLOCKS structure.  Clock_nanosleep is in
- *          there, but the code ignors it.
+ *          there, but the code ignores it.
  *
  * Permissions: It is assumed that the clock_settime() function defined
  *	    for each clock will take care of permission checks.	 Some
@@ -193,12 +189,12 @@ static struct k_clock_abs abs_list = {.list = LIST_HEAD_INIT(abs_list.list),
 #define p_timer_del(clock,a) \
 		if_clock_do((clock)->timer_del, do_timer_delete, (a))
 
-void register_posix_clock(int clock_id, struct k_clock *new_clock);
 static int do_posix_gettime(struct k_clock *clock, struct timespec *tp);
 static u64 do_posix_clock_monotonic_gettime_parts(
 	struct timespec *tp, struct timespec *mo);
 int do_posix_clock_monotonic_gettime(struct timespec *tp);
-int do_posix_clock_monotonic_settime(struct timespec *tp);
+static int do_posix_clock_process_gettime(struct timespec *tp);
+static int do_posix_clock_thread_gettime(struct timespec *tp);
 static struct k_itimer *lock_timer(timer_t timer_id, unsigned long *flags);
 
 static inline void unlock_timer(struct k_itimer *timr, unsigned long flags)
@@ -217,11 +213,27 @@ static __init int init_posix_timers(void)
 	struct k_clock clock_monotonic = {.res = CLOCK_REALTIME_RES,
 		.abs_struct = NULL,
 		.clock_get = do_posix_clock_monotonic_gettime,
-		.clock_set = do_posix_clock_monotonic_settime
+		.clock_set = do_posix_clock_nosettime
+	};
+	struct k_clock clock_thread = {.res = CLOCK_REALTIME_RES,
+		.abs_struct = NULL,
+		.clock_get = do_posix_clock_thread_gettime,
+		.clock_set = do_posix_clock_nosettime,
+		.timer_create = do_posix_clock_notimer_create,
+		.nsleep = do_posix_clock_nonanosleep
+	};
+	struct k_clock clock_process = {.res = CLOCK_REALTIME_RES,
+		.abs_struct = NULL,
+		.clock_get = do_posix_clock_process_gettime,
+		.clock_set = do_posix_clock_nosettime,
+		.timer_create = do_posix_clock_notimer_create,
+		.nsleep = do_posix_clock_nonanosleep
 	};
 
 	register_posix_clock(CLOCK_REALTIME, &clock_realtime);
 	register_posix_clock(CLOCK_MONOTONIC, &clock_monotonic);
+	register_posix_clock(CLOCK_PROCESS_CPUTIME_ID, &clock_process);
+	register_posix_clock(CLOCK_THREAD_CPUTIME_ID, &clock_thread);
 
 	posix_timers_cache = kmem_cache_create("posix_timers_cache",
 					sizeof (struct k_itimer), 0, 0, NULL, NULL);
@@ -573,6 +585,10 @@ sys_timer_create(clockid_t which_clock,
 				!posix_clocks[which_clock].res)
 		return -EINVAL;
 
+	if (posix_clocks[which_clock].timer_create)
+		return posix_clocks[which_clock].timer_create(which_clock,
+				timer_event_spec, created_timer_id);
+
 	new_timer = alloc_posix_timer();
 	if (unlikely(!new_timer))
 		return -EAGAIN;
@@ -1218,16 +1234,87 @@ int do_posix_clock_monotonic_gettime(struct timespec *tp)
 	return 0;
 }
 
-int do_posix_clock_monotonic_settime(struct timespec *tp)
+int do_posix_clock_nosettime(struct timespec *tp)
 {
 	return -EINVAL;
 }
 
+int do_posix_clock_notimer_create(int which_clock,
+		struct sigevent __user *timer_event_spec,
+		timer_t __user *created_timer_id) {
+	return -EINVAL;
+}
+
+int do_posix_clock_nonanosleep(int which_lock, int flags,struct timespec * t) {
+/* Single Unix specficiation says to return ENOTSUP but we do not have that */
+	return -EINVAL;
+}
+
+static unsigned long process_ticks(task_t *p) {
+	unsigned long ticks;
+	task_t *t;
+
+	spin_lock(&p->sighand->siglock);
+	/* The signal structure is shared between all threads */
+	ticks = p->signal->utime + p->signal->stime;
+
+	/* Add up the cpu time for all the still running threads of this process */
+	t = p;
+	do {
+		ticks += t->utime + t->stime;
+		t = next_thread(t);
+	} while (t != p);
+
+	spin_unlock(&p->sighand->siglock);
+	return ticks;
+}
+
+static inline unsigned long thread_ticks(task_t *p) {
+	return p->utime + current->stime;
+}
+
+/*
+ * Single Unix Specification V3:
+ *
+ * Implementations shall also support the special clockid_t value
+ * CLOCK_THREAD_CPUTIME_ID, which represents the CPU-time clock of the calling
+ * thread when invoking one of the clock_*() or timer_*() functions. For these
+ * clock IDs, the values returned by clock_gettime() and specified by
+ * clock_settime() shall represent the amount of execution time of the thread
+ * associated with the clock.
+ */
+static int do_posix_clock_thread_gettime(struct timespec *tp)
+{
+	jiffies_to_timespec(thread_ticks(current), tp);
+	return 0;
+}
+
+/*
+ * Single Unix Specification V3:
+ *
+ * Implementations shall also support the special clockid_t value
+ * CLOCK_PROCESS_CPUTIME_ID, which represents the CPU-time clock of the
+ * calling process when invoking one of the clock_*() or timer_*() functions.
+ * For these clock IDs, the values returned by clock_gettime() and specified
+ * by clock_settime() represent the amount of execution time of the process
+ * associated with the clock.
+ */
+
+static int do_posix_clock_process_gettime(struct timespec *tp)
+{
+	jiffies_to_timespec(process_ticks(current), tp);
+	return 0;
+}
+
 asmlinkage long
 sys_clock_settime(clockid_t which_clock, const struct timespec __user *tp)
 {
 	struct timespec new_tp;
 
+	/* Cannot set process specific clocks */
+	if (which_clock<0)
+		return -EINVAL;
+
 	if ((unsigned) which_clock >= MAX_CLOCKS ||
 					!posix_clocks[which_clock].res)
 		return -EINVAL;
@@ -1245,6 +1332,29 @@ sys_clock_gettime(clockid_t which_clock, struct timespec __user *tp)
 	struct timespec rtn_tp;
 	int error = 0;
 
+	/* Process process specific clocks */
+	if (which_clock < 0) {
+		task_t *t;
+		int pid = -which_clock;
+
+		if (pid < PID_MAX_LIMIT) {
+			if ((t = find_task_by_pid(pid))) {
+				jiffies_to_timespec(process_ticks(t), tp);
+				return 0;
+			}
+			return -EINVAL;
+		}
+		if (pid < 2*PID_MAX_LIMIT) {
+			if ((t = find_task_by_pid(pid - PID_MAX_LIMIT))) {
+				jiffies_to_timespec(thread_ticks(t), tp);
+				return 0;
+			}
+			return -EINVAL;
+		}
+		/* More process specific clocks could follow here */
+		return -EINVAL;
+	}
+
 	if ((unsigned) which_clock >= MAX_CLOCKS ||
 					!posix_clocks[which_clock].res)
 		return -EINVAL;
@@ -1263,6 +1373,9 @@ sys_clock_getres(clockid_t which_clock, struct timespec __user *tp)
 {
 	struct timespec rtn_tp;
 
+	/* All process clocks have the resolution of CLOCK_PROCESS_CPUTIME_ID */
+	if (which_clock < 0 ) which_clock = CLOCK_PROCESS_CPUTIME_ID;
+
 	if ((unsigned) which_clock >= MAX_CLOCKS ||
 					!posix_clocks[which_clock].res)
 		return -EINVAL;
@@ -1409,7 +1522,10 @@ sys_clock_nanosleep(clockid_t which_clock, int flags,
 	if ((unsigned) t.tv_nsec >= NSEC_PER_SEC || t.tv_sec < 0)
 		return -EINVAL;
 
-	ret = do_clock_nanosleep(which_clock, flags, &t);
+	if (posix_clocks[which_clock].nsleep)
+		ret = posix_clocks[which_clock].nsleep(which_clock, flags, &t);
+	else
+		ret = do_clock_nanosleep(which_clock, flags, &t);
 	/*
 	 * Do this here as do_clock_nanosleep does not have the real address
 	 */