[PATCH 3/3] High-res-timers part 3 (posix to hrposix) take 13

[george anzinger]

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This patch adds the two POSIX clocks CLOCK_REALTIME_HR and
CLOCK_MONOTONIC_HR to the posix clocks & timers package.  A
small change is made in sched.h and the rest of the patch is
against .../kernel/posix_timers.c.

Concerns and on going work:

The kernel interface to the signal delivery code and it's
need for &regs causes the nanosleep and clock_nanosleep code
to be very messy.  The supplied interface works for the x86
platform and provides the hooks for other platforms to
connect (see .../include/asm-i386/signal.h for details), but
a much cleaner solution is desired.

This patch guards against overload by limiting the repeat
interval of timers to a fixed value (currently 0.5 ms).  A
suggested change, and one I am working on, is to not put the
timer back in the timer list until the user's signal handler
has completed processing the current expiry.  This requires
a call back from the signal completion code, again a
platform dependent thing, BUT it has the advantage of
automatically adjusting the interval to match the hardware,
the system overhead and the current load.  In all cases, the
standard says we need to account for the overruns, but by
not getting the timer interrupt code involved in useless
spinning, we just bump the overrun, saving a LOT of
overhead.

This patch fixes the high resolution timer resolution at 1
micro second.  Should this number be a CONFIG option?

I think it would be a "good thing"=AE to move the NTP stuff to
the jiffies clock.  This would allow the wall clock/ jiffies
clock difference to be a "fixed value" so that code that
needed this would not have to read two clocks.  Setting the
wall clock would then just be an adjustment to this "fixed
value".  It would also eliminate the problem of asking for a
wall clock offset and getting a jiffies clock offset.  This
issue is what causes the current 2.5.46 system to fail the
simple:

time sleep 60

test (any value less than 60 seconds violates the standard
in that it implies a timer expired early).

Patch is against 2.5.46-bk1

These patches as well as the POSIX clocks & timers patch are
available on the project site:
http://sourceforge.net/projects/high-res-timers/

The 3 parts to the high res timers are:
 core      The core kernel (i.e. platform independent)
changes
 i386      The high-res changes for the i386 (x86) platform
*posixhr   The changes to the POSIX clocks & timers patch to
           use high-res timers

Please apply.
-- =

George Anzinger   [e-mail]
High-res-timers: =

http://sourceforge.net/projects/high-res-timers/
Preemption patch:
http://www.kernel.org/pub/linux/kernel/people/rml
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diff -urP -I \$Id:.*Exp \$ -X /usr/src/patch.exclude linux-2.5.46-bk1-i386/include/linux/sched.h linux/include/linux/sched.h
--- linux-2.5.46-bk1-i386/include/linux/sched.h	Tue Nov  5 20:56:36 2002
+++ linux/include/linux/sched.h	Tue Nov  5 21:22:58 2002
@@ -281,6 +281,9 @@
 	int it_sigev_signo;		 /* signo word of sigevent struct */
 	sigval_t it_sigev_value;	 /* value word of sigevent struct */
 	unsigned long it_incr;		/* interval specified in jiffies */
+#ifdef CONFIG_HIGH_RES_TIMERS
+        int it_sub_incr;                /* sub jiffie part of interval */
+#endif
 	struct task_struct *it_process;	/* process to send signal to */
 	struct timer_list it_timer;
 };
diff -urP -I \$Id:.*Exp \$ -X /usr/src/patch.exclude linux-2.5.46-bk1-i386/kernel/posix-timers.c linux/kernel/posix-timers.c
--- linux-2.5.46-bk1-i386/kernel/posix-timers.c	Tue Nov  5 20:56:36 2002
+++ linux/kernel/posix-timers.c	Tue Nov  5 21:22:58 2002
@@ -23,6 +23,7 @@
 #include <linux/posix-timers.h>
 #include <linux/compiler.h>
 #include <linux/id_reuse.h>
+#include <linux/hrtime.h>
 
 #ifndef div_long_long_rem
 #include <asm/div64.h>
@@ -33,7 +34,7 @@
 		       result; })
 
 #endif	 /* ifndef div_long_long_rem */
-
+#define CONFIGURE_MIN_INTERVAL 500000
 /*
  * Management arrays for POSIX timers.	 Timers are kept in slab memory
  * Timer ids are allocated by an external routine that keeps track of the
@@ -156,6 +157,7 @@
 
 int do_posix_clock_monotonic_settime(struct timespec *tp);
 
+IF_HIGH_RES(static int high_res_guard = 0;)
 /* 
  * Initialize everything, well, just everything in Posix clocks/timers ;)
  */
@@ -174,6 +176,15 @@
 	posix_timers_cache = kmem_cache_create("posix_timers_cache",
 		sizeof(struct k_itimer), 0, 0, 0, 0);
 	idr_init(&posix_timers_id);
+	IF_HIGH_RES(clock_realtime.res = CONFIG_HIGH_RES_RESOLUTION;
+		    register_posix_clock(CLOCK_REALTIME_HR,&clock_realtime);
+		    clock_monotonic.res = CONFIG_HIGH_RES_RESOLUTION;
+		    register_posix_clock(CLOCK_MONOTONIC_HR,&clock_monotonic);
+		    high_res_guard = nsec_to_arch_cycles(CONFIGURE_MIN_INTERVAL);
+		);
+#ifdef	 final_clock_init
+	final_clock_init();	  // defined by arch header file
+#endif
 	return 0;
 }
 
@@ -214,8 +225,23 @@
 	 * We trust that the optimizer will use the remainder from the 
 	 * above div in the following operation as long as they are close. 
 	 */
-	return	0;
+	return	 (nsec_to_arch_cycles(nsec % (NSEC_PER_SEC / HZ)));
+}
+#ifdef CONFIG_HIGH_RES_TIMERS
+static void tstotimer(struct itimerspec * time, struct k_itimer * timer)
+{
+	int res = posix_clocks[timer->it_clock].res;
+
+	timer->it_timer.sub_expires = tstojiffie(&time->it_value,
+						 res,
+						 &timer->it_timer.expires);
+	timer->it_sub_incr = tstojiffie(&time->it_interval,
+					res,
+					(unsigned long*) &timer->it_incr);
+	if ((unsigned long)timer->it_incr > MAX_JIFFY_OFFSET)
+		timer->it_incr = MAX_JIFFY_OFFSET;
 }
+#else
 static void tstotimer(struct itimerspec * time, struct k_itimer * timer)
 {
 	int res = posix_clocks[timer->it_clock].res;
@@ -228,6 +254,7 @@
 }
  
 
+#endif
 
 /* PRECONDITION:
  * timr->it_lock must be locked
@@ -265,6 +292,47 @@
 	}
 }
 
+#ifdef CONFIG_HIGH_RES_TIMERS
+/*
+ * This bit of code is to protect the system from being consumed by
+ * repeating timer expirations.	 We detect overrun and adjust the
+ * next time to be at least high_res_guard out. We clock the overrun
+ * but only AFTER the next expire as it has not really happened yet.
+ *
+ * Careful, only do this if the timer repeat time is less than
+ * high_res_guard AND we have fallen behind.
+
+ * All this will go away with signal delivery callback...
+ */
+
+static inline void  do_overrun_protect(struct k_itimer *timr)
+{
+	timr->it_overrun_deferred = 0;
+
+	if (! timr->it_incr &&
+	    (high_res_guard > timr->it_sub_incr)){
+		int offset = quick_update_jiffies_sub( timr->it_timer.expires);
+
+		offset -= timr->it_timer.sub_expires;
+		// touch_nmi_watchdog();
+		offset += high_res_guard;
+		if (offset <= 0){
+			return;
+		}
+		// expire time is in the past (or within the guard window)
+
+		timr->it_overrun_deferred = (offset / timr->it_sub_incr) - 1;
+		timr->it_timer.sub_expires += 
+			offset - (offset % timr->it_sub_incr);
+				     
+		while ((timr->it_timer.sub_expires -  cycles_per_jiffies) >= 0){
+			timr->it_timer.sub_expires -= cycles_per_jiffies;
+			timr->it_timer.expires++;
+		}
+	}
+}
+
+#endif
 /* 
  * Notify the task and set up the timer for the next expiration (if applicable).
  * This function requires that the k_itimer structure it_lock is taken.
@@ -277,7 +345,8 @@
 
 	/* Set up the timer for the next interval (if there is one) */
 	if ((interval = timr->it_incr) == 0){
-		{
+		IF_HIGH_RES(if(timr->it_sub_incr == 0)
+			){
 			set_timer_inactive(timr);
 			return;
 		}
@@ -285,6 +354,13 @@
 	if (interval > (unsigned long) LONG_MAX)
 		interval = LONG_MAX;
 	timr->it_timer.expires += interval;
+	IF_HIGH_RES(timr->it_timer.sub_expires += timr->it_sub_incr;
+		    if ((timr->it_timer.sub_expires - cycles_per_jiffies) >= 0){
+			    timr->it_timer.sub_expires -= cycles_per_jiffies;
+			    timr->it_timer.expires++;
+		    }
+		    do_overrun_protect(timr);
+		);
 	add_timer(&timr->it_timer);
 }
 
@@ -543,17 +619,39 @@
 
 	do {
 		expires = timr->it_timer.expires;  
+		IF_HIGH_RES(sub_expires = timr->it_timer.sub_expires);
 	} while ((volatile long)(timr->it_timer.expires) != expires);
 
+	IF_HIGH_RES(write_lock(&xtime_lock);
+		    update_jiffies_sub());
 	if (expires && timer_pending(&timr->it_timer)){
 		expires -= jiffies;
+		IF_HIGH_RES(sub_expires -=  sub_jiffie());
 	}else{
 		sub_expires = expires = 0;
 	}
+	IF_HIGH_RES( write_unlock(&xtime_lock));
 
 	jiffies_to_timespec(expires, &cur_setting->it_value);
 	jiffies_to_timespec(timr->it_incr, &cur_setting->it_interval);
 
+	IF_HIGH_RES(cur_setting->it_value.tv_nsec += 
+		    arch_cycles_to_nsec( sub_expires);
+		    if (cur_setting->it_value.tv_nsec < 0){
+			    cur_setting->it_value.tv_nsec += NSEC_PER_SEC;
+			    cur_setting->it_value.tv_sec--;
+		    }
+		    if ((cur_setting->it_value.tv_nsec - NSEC_PER_SEC) >= 0){
+			    cur_setting->it_value.tv_nsec -= NSEC_PER_SEC;
+			    cur_setting->it_value.tv_sec++;
+		    }
+		    cur_setting->it_interval.tv_nsec += 
+		    arch_cycles_to_nsec(timr->it_sub_incr);
+		    if ((cur_setting->it_interval.tv_nsec - NSEC_PER_SEC) >= 0){
+			    cur_setting->it_interval.tv_nsec -= NSEC_PER_SEC;
+			    cur_setting->it_interval.tv_sec++;
+		    }
+		);	     
 	if (cur_setting->it_value.tv_sec < 0){
 		cur_setting->it_value.tv_nsec = 1;
 		cur_setting->it_value.tv_sec = 0;
@@ -699,6 +797,7 @@
 
 	/* disable the timer */
 	timr->it_incr = 0;
+	IF_HIGH_RES(timr->it_sub_incr = 0);
 	/* 
 	 * careful here.  If smp we could be in the "fire" routine which will
 	 * be spinning as we hold the lock.  But this is ONLY an SMP issue.
@@ -723,6 +822,7 @@
 	if ((new_setting->it_value.tv_sec == 0) &&
 	    (new_setting->it_value.tv_nsec == 0)) {
 		timr->it_timer.expires = 0;
+		IF_HIGH_RES(timr->it_timer.sub_expires = 0 );
 		return 0;
 	}
 
@@ -743,10 +843,12 @@
 	 * For some reason the timer does not fire immediately if expires is
 	 * equal to jiffies, so the timer callback function is called directly.
 	 */
+#ifndef	 CONFIG_HIGH_RES_TIMERS
 	if (timr->it_timer.expires == jiffies) {
 		posix_timer_fire(timr);
 		return 0;
 	}
+#endif
 	timr->it_overrun_deferred = 
 		timr->it_overrun_last = 
 		timr->it_overrun = 0;
@@ -808,6 +910,7 @@
 static inline int do_timer_delete(struct k_itimer  *timer)
 {
 	timer->it_incr = 0;
+	IF_HIGH_RES(timer->it_sub_incr = 0);
 #ifdef CONFIG_SMP
 	if ( timer_active(timer) && ! del_timer(&timer->it_timer)){
 		/*
@@ -905,8 +1008,25 @@
 		return clock->clock_get(tp);
 	}
 
+#ifdef CONFIG_HIGH_RES_TIMERS
+	{
+		unsigned long flags;
+		write_lock_irqsave(&xtime_lock, flags);
+		update_jiffies_sub();
+		update_real_wall_time();  
+		tp->tv_sec = xtime.tv_sec;
+		tp->tv_nsec = xtime.tv_nsec;
+		tp->tv_nsec += arch_cycles_to_nsec(sub_jiffie());
+		write_unlock_irqrestore(&xtime_lock, flags);
+		if ( tp->tv_nsec >  NSEC_PER_SEC ){
+			tp->tv_nsec -= NSEC_PER_SEC ;
+			tp->tv_sec++;
+		}
+	}
+#else
 	do_gettimeofday((struct timeval*)tp);
 	tp->tv_nsec *= NSEC_PER_USEC;
+#endif
 	return 0;
 }
 
@@ -921,8 +1041,9 @@
 {
 	long sub_sec;
 	u64 jiffies_64_f;
+	IF_HIGH_RES(long sub_jiff_offset;)
 
-#if (BITS_PER_LONG > 32) 
+#if (BITS_PER_LONG > 32) && !defined(CONFIG_HIGH_RES_TIMERS)
 
 	jiffies_64_f = jiffies_64;
 
@@ -936,6 +1057,8 @@
 		read_lock_irqsave(&xtime_lock, flags);
 		jiffies_64_f = jiffies_64;
 
+		IF_HIGH_RES(sub_jiff_offset =	
+			    quick_update_jiffies_sub(jiffies));
 
 		read_unlock_irqrestore(&xtime_lock, flags);
 	}
@@ -944,14 +1067,34 @@
 	do {
 		jiffies_f = jiffies;
 		barrier();
+		IF_HIGH_RES(
+			sub_jiff_offset = 
+			quick_update_jiffies_sub(jiffies_f));
 		jiffies_64_f = jiffies_64;
 	} while (unlikely(jiffies_f != jiffies));
 
+#else /* 64 bit long and high-res but no SMP if I did the Venn right */
+	do {
+		jiffies_64_f = jiffies_64;
+		barrier();
+		sub_jiff_offset = quick_update_jiffies_sub(jiffies_64_f);
+	} while (unlikely(jiffies_64_f != jiffies_64));
 
 #endif
-	tp->tv_sec = div_long_long_rem(jiffies_64_f,HZ,&sub_sec);
+	/*
+	 * Remember that quick_update_jiffies_sub() can return more
+	 * than a jiffies worth of cycles...
+	 */
+	IF_HIGH_RES(
+		while ( unlikely(sub_jiff_offset > cycles_per_jiffies)){
+			sub_jiff_offset -= cycles_per_jiffies;
+			jiffies_64_f++;
+		}
+		)
+		tp->tv_sec = div_long_long_rem(jiffies_64_f,HZ,&sub_sec);
 
 	tp->tv_nsec = sub_sec * (NSEC_PER_SEC / HZ);
+	IF_HIGH_RES(tp->tv_nsec += arch_cycles_to_nsec(sub_jiff_offset));
 	return 0;
 }
 
@@ -1110,6 +1253,7 @@
 			 * del_timer_sync() will return 0, thus
 			 * active is zero... and so it goes.
 			 */
+			IF_HIGH_RES(new_timer.sub_expires = )
 
 				tstojiffie(&t,
 					   posix_clocks[which_clock].res,
@@ -1131,9 +1275,15 @@
 	}
 	if (active && rmtp ) {
 		unsigned long jiffies_f = jiffies;
+		IF_HIGH_RES(
+			long sub_jiff = 
+			quick_update_jiffies_sub(jiffies_f));
 
 		jiffies_to_timespec(new_timer.expires - jiffies_f, &t);
 
+		IF_HIGH_RES(t.tv_nsec += 
+			    arch_cycles_to_nsec(new_timer.sub_expires -
+						sub_jiff));
 		while (t.tv_nsec < 0){
 			t.tv_nsec += NSEC_PER_SEC;
 			t.tv_sec--;
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