[MINOR] freq_ctr: add new types and functions for periods different from 1s

Some freq counters will have to work on periods different from 1 second.
The original freq counters rely on the period to be exactly one second.
The new ones (freq_ctr_period) let the user define the period in ticks,
and all computations are operated over that period. When reading a value,
it indicates the amount of events over that period too.

include/proto/freq_ctr.h

@@ -56,6 +56,41 @@ static inline void update_freq_ctr(struct freq_ctr *ctr, unsigned int inc)
 	/* Note: later we may want to propagate the update to other counters */
 }
 
+/* Rotate a frequency counter when current period is over. Must not be called
+ * during a valid period. It is important that it correctly initializes a null
+ * area. This one works on frequency counters which have a period different
+ * from one second.
+ */
+static inline void rotate_freq_ctr_period(struct freq_ctr_period *ctr,
+					  unsigned int period)
+{
+	ctr->prev_ctr = ctr->curr_ctr;
+	ctr->curr_tick += period;
+	if (likely(now_ms - ctr->curr_tick >= period)) {
+		/* we missed at least two periods */
+		ctr->prev_ctr = 0;
+		ctr->curr_tick = now_ms;
+	}
+	ctr->curr_ctr = 0; /* leave it at the end to help gcc optimize it away */
+}
+
+/* Update a frequency counter by <inc> incremental units. It is automatically
+ * rotated if the period is over. It is important that it correctly initializes
+ * a null area. This one works on frequency counters which have a period
+ * different from one second.
+ */
+static inline void update_freq_ctr_period(struct freq_ctr_period *ctr,
+					  unsigned int period, unsigned int inc)
+{
+	if (likely(now_ms - ctr->curr_tick < period)) {
+		ctr->curr_ctr += inc;
+		return;
+	}
+	rotate_freq_ctr_period(ctr, period);
+	ctr->curr_ctr = inc;
+	/* Note: later we may want to propagate the update to other counters */
+}
+
 /* Read a frequency counter taking history into account for missing time in
  * current period.
  */
@@ -75,6 +110,11 @@ unsigned int freq_ctr_remain(struct freq_ctr *ctr, unsigned int freq, unsigned i
  */
 unsigned int next_event_delay(struct freq_ctr *ctr, unsigned int freq, unsigned int pend);
 
+/* process freq counters over configurable periods */
+unsigned int read_freq_ctr_period(struct freq_ctr_period *ctr, unsigned int period);
+unsigned int freq_ctr_remain_period(struct freq_ctr_period *ctr, unsigned int period,
+				    unsigned int freq, unsigned int pend);
+
 #endif /* _PROTO_FREQ_CTR_H */
 
 /*

include/types/freq_ctr.h

@@ -1,35 +1,50 @@
 /*
-  include/types/freq_ctr.h
+ * include/types/freq_ctr.h
-  This file contains structure declarations for frequency counters.
+ * This file contains structure declarations for frequency counters.
-
+ *
-  Copyright (C) 2000-2009 Willy Tarreau - w@1wt.eu
+ * Copyright (C) 2000-2010 Willy Tarreau - w@1wt.eu
-  
+ *
-  This library is free software; you can redistribute it and/or
+ * This library is free software; you can redistribute it and/or
-  modify it under the terms of the GNU Lesser General Public
+ * modify it under the terms of the GNU Lesser General Public
-  License as published by the Free Software Foundation, version 2.1
+ * License as published by the Free Software Foundation, version 2.1
-  exclusively.
+ * exclusively.
-
+ *
-  This library is distributed in the hope that it will be useful,
+ * This library is distributed in the hope that it will be useful,
-  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-  Lesser General Public License for more details.
+ * Lesser General Public License for more details.
-
+ *
-  You should have received a copy of the GNU Lesser General Public
+ * You should have received a copy of the GNU Lesser General Public
-  License along with this library; if not, write to the Free Software
+ * License along with this library; if not, write to the Free Software
-  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
-*/
+ */
 
 #ifndef _TYPES_FREQ_CTR_H
 #define _TYPES_FREQ_CTR_H
 
 #include <common/config.h>
 
+/* The implicit freq_ctr counter counts a rate of events per second. It is the
+ * preferred form to count rates over a one-second period, because it does not
+ * involve any divide.
+ */
 struct freq_ctr {
 	unsigned int curr_sec; /* start date of current period (seconds from now.tv_sec) */
 	unsigned int curr_ctr; /* cumulated value for current period */
 	unsigned int prev_ctr; /* value for last period */
 };
 
+/* The generic freq_ctr_period counter counts a rate of events per period, where
+ * the period has to be known by the user. The period is measured in ticks and
+ * must be at least 2 ticks long. This form is slightly more CPU intensive than
+ * the per-second form.
+ */
+struct freq_ctr_period {
+	unsigned int curr_tick; /* start date of current period (wrapping ticks) */
+	unsigned int curr_ctr;  /* cumulated value for current period */
+	unsigned int prev_ctr;  /* value for last period */
+};
+
 #endif /* _TYPES_FREQ_CTR_H */
 
 /*

src/freq_ctr.c

@@ -1,7 +1,7 @@
 /*
  * Event rate calculation functions.
  *
- * Copyright 2000-2009 Willy Tarreau <w@1wt.eu>
+ * Copyright 2000-2010 Willy Tarreau <w@1wt.eu>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -110,6 +110,82 @@ unsigned int next_event_delay(struct freq_ctr *ctr, unsigned int freq, unsigned
 	return MAX(wait, 1);
 }
 
+/* Reads a frequency counter taking history into account for missing time in
+ * current period. The period has to be passed in number of ticks and must
+ * match the one used to feed the counter. The counter value is reported for
+ * current date (now_ms). The return value has the same precision as one input
+ * data sample, so low rates over the period will be inaccurate but still
+ * appropriate for max checking. One trick we use for low values is to specially
+ * handle the case where the rate is between 0 and 1 in order to avoid flapping
+ * while waiting for the next event.
+ *
+ * For immediate limit checking, it's recommended to use freq_ctr_period_remain()
+ * instead which does not have the flapping correction, so that even frequencies
+ * as low as one event/period are properly handled.
+ *
+ * For measures over a 1-second period, it's better to use the implicit functions
+ * above.
+ */
+unsigned int read_freq_ctr_period(struct freq_ctr_period *ctr, unsigned int period)
+{
+	unsigned int curr, past;
+	unsigned int remain;
+
+	curr = ctr->curr_ctr;
+	past = ctr->prev_ctr;
+
+	remain = ctr->curr_tick + period - now_ms;
+	if (unlikely((int)remain < 0)) {
+		/* We're past the first period, check if we can still report a
+		 * part of last period or if we're too far away.
+		 */
+		remain += period;
+		if ((int)remain < 0)
+			return 0;
+		past = curr;
+		curr = 0;
+	}
+	if (past <= 1 && !curr)
+		return past; /* very low rate, avoid flapping */
+
+	curr += div64_32((unsigned long long)past * remain, period);
+	return curr;
+}
+
+/* Returns the number of remaining events that can occur on this freq counter
+ * while respecting <freq> events per period, and taking into account that
+ * <pend> events are already known to be pending. Returns 0 if limit was reached.
+ */
+unsigned int freq_ctr_remain_period(struct freq_ctr_period *ctr, unsigned int period,
+				    unsigned int freq, unsigned int pend)
+{
+	unsigned int curr, past;
+	unsigned int remain;
+
+	curr = ctr->curr_ctr;
+	past = ctr->prev_ctr;
+
+	remain = ctr->curr_tick + period - now_ms;
+	if (likely((int)remain < 0)) {
+		/* We're past the first period, check if we can still report a
+		 * part of last period or if we're too far away.
+		 */
+		past = curr;
+		curr = 0;
+		remain += period;
+		if ((int)remain < 0)
+			past = 0;
+	}
+	if (likely(past))
+		curr += div64_32((unsigned long long)past * remain, period);
+
+	curr += pend;
+	freq -= curr;
+	if ((int)freq < 0)
+		freq = 0;
+	return freq;
+}
+
 
 /*
  * Local variables: