From: Michal Schmidt <mschmidt@redhat.com>
Date: Fri, 3 Sep 2010 19:57:59 -0400
Subject: [misc] add round_jiffies_up and related routines
Message-id: <20100903195758.7750.97816.stgit@localhost6.localdomain6>
Patchwork-id: 28129
O-Subject: [RHEL5.6 BZ556476 PATCH 3/6] Add round_jiffies_up and related routines
Bugzilla: 556476
RH-Acked-by: David S. Miller <davem@redhat.com>
RH-Acked-by: Thomas Graf <tgraf@redhat.com>

BZ: https://bugzilla.redhat.com/show_bug.cgi?id=556476

This adds useful routines to timer.c:
 EXPORT_SYMBOL_GPL(__round_jiffies_up);
 EXPORT_SYMBOL_GPL(__round_jiffies_up_relative);
 EXPORT_SYMBOL_GPL(round_jiffies_up);
 EXPORT_SYMBOL_GPL(round_jiffies_up_relative);

Upstream commit 9c133c469d38043d5aadaa03f2fb840d88d1cf4f.
Original description:

 This patch (as1158b) adds round_jiffies_up() and friends.  These
 routines work like the analogous round_jiffies() functions, except
 that they will never round down.

 The new routines will be useful for timeouts where we don't care
 exactly when the timer expires, provided it doesn't expire too soon.

 Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
 Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/include/linux/timer.h b/include/linux/timer.h
index 0a87f6d..dff3bc2 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -103,4 +103,9 @@ unsigned long __round_jiffies_relative(unsigned long j, int cpu);
 unsigned long round_jiffies(unsigned long j);
 unsigned long round_jiffies_relative(unsigned long j);
 
+unsigned long __round_jiffies_up(unsigned long j, int cpu);
+unsigned long __round_jiffies_up_relative(unsigned long j, int cpu);
+unsigned long round_jiffies_up(unsigned long j);
+unsigned long round_jiffies_up_relative(unsigned long j);
+
 #endif
diff --git a/kernel/timer.c b/kernel/timer.c
index dc73f0f..0e2fe5d 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -89,27 +89,8 @@ tvec_base_t boot_tvec_bases;
 EXPORT_SYMBOL(boot_tvec_bases);
 static DEFINE_PER_CPU(tvec_base_t *, tvec_bases) = &boot_tvec_bases;
 
-/**
- * __round_jiffies - function to round jiffies to a full second
- * @j: the time in (absolute) jiffies that should be rounded
- * @cpu: the processor number on which the timeout will happen
- *
- * __round_jiffies() rounds an absolute time in the future (in jiffies)
- * up or down to (approximately) full seconds. This is useful for timers
- * for which the exact time they fire does not matter too much, as long as
- * they fire approximately every X seconds.
- *
- * By rounding these timers to whole seconds, all such timers will fire
- * at the same time, rather than at various times spread out. The goal
- * of this is to have the CPU wake up less, which saves power.
- *
- * The exact rounding is skewed for each processor to avoid all
- * processors firing at the exact same time, which could lead
- * to lock contention or spurious cache line bouncing.
- *
- * The return value is the rounded version of the @j parameter.
- */
-unsigned long __round_jiffies(unsigned long j, int cpu)
+static unsigned long round_jiffies_common(unsigned long j, int cpu,
+		bool force_up)
 {
 	int rem;
 	unsigned long original = j;
@@ -131,8 +112,9 @@ unsigned long __round_jiffies(unsigned long j, int cpu)
 	 * due to delays of the timer irq, long irq off times etc etc) then
 	 * we should round down to the whole second, not up. Use 1/4th second
 	 * as cutoff for this rounding as an extreme upper bound for this.
+	 * But never round down if @force_up is set.
 	 */
-	if (rem < HZ/4) /* round down */
+	if (rem < HZ/4 && !force_up) /* round down */
 		j = j - rem;
 	else /* round up */
 		j = j - rem + HZ;
@@ -144,6 +126,31 @@ unsigned long __round_jiffies(unsigned long j, int cpu)
 		return original;
 	return j;
 }
+
+/**
+ * __round_jiffies - function to round jiffies to a full second
+ * @j: the time in (absolute) jiffies that should be rounded
+ * @cpu: the processor number on which the timeout will happen
+ *
+ * __round_jiffies() rounds an absolute time in the future (in jiffies)
+ * up or down to (approximately) full seconds. This is useful for timers
+ * for which the exact time they fire does not matter too much, as long as
+ * they fire approximately every X seconds.
+ *
+ * By rounding these timers to whole seconds, all such timers will fire
+ * at the same time, rather than at various times spread out. The goal
+ * of this is to have the CPU wake up less, which saves power.
+ *
+ * The exact rounding is skewed for each processor to avoid all
+ * processors firing at the exact same time, which could lead
+ * to lock contention or spurious cache line bouncing.
+ *
+ * The return value is the rounded version of the @j parameter.
+ */
+unsigned long __round_jiffies(unsigned long j, int cpu)
+{
+	return round_jiffies_common(j, cpu, false);
+}
 EXPORT_SYMBOL_GPL(__round_jiffies);
 
 /**
@@ -168,13 +175,10 @@ EXPORT_SYMBOL_GPL(__round_jiffies);
  */
 unsigned long __round_jiffies_relative(unsigned long j, int cpu)
 {
-	/*
-	 * In theory the following code can skip a jiffy in case jiffies
-	 * increments right between the addition and the later subtraction.
-	 * However since the entire point of this function is to use approximate
-	 * timeouts, it's entirely ok to not handle that.
-	 */
-	return  __round_jiffies(j + jiffies, cpu) - jiffies;
+	unsigned long j0 = jiffies;
+
+	/* Use j0 because jiffies might change while we run */
+	return round_jiffies_common(j + j0, cpu, false) - j0;
 }
 EXPORT_SYMBOL_GPL(__round_jiffies_relative);
 
@@ -195,7 +199,7 @@ EXPORT_SYMBOL_GPL(__round_jiffies_relative);
  */
 unsigned long round_jiffies(unsigned long j)
 {
-	return __round_jiffies(j, raw_smp_processor_id());
+	return round_jiffies_common(j, raw_smp_processor_id(), false);
 }
 EXPORT_SYMBOL_GPL(round_jiffies);
 
@@ -220,6 +224,71 @@ unsigned long round_jiffies_relative(unsigned long j)
 }
 EXPORT_SYMBOL_GPL(round_jiffies_relative);
 
+/**
+ * __round_jiffies_up - function to round jiffies up to a full second
+ * @j: the time in (absolute) jiffies that should be rounded
+ * @cpu: the processor number on which the timeout will happen
+ *
+ * This is the same as __round_jiffies() except that it will never
+ * round down.  This is useful for timeouts for which the exact time
+ * of firing does not matter too much, as long as they don't fire too
+ * early.
+ */
+unsigned long __round_jiffies_up(unsigned long j, int cpu)
+{
+	return round_jiffies_common(j, cpu, true);
+}
+EXPORT_SYMBOL_GPL(__round_jiffies_up);
+
+/**
+ * __round_jiffies_up_relative - function to round jiffies up to a full second
+ * @j: the time in (relative) jiffies that should be rounded
+ * @cpu: the processor number on which the timeout will happen
+ *
+ * This is the same as __round_jiffies_relative() except that it will never
+ * round down.  This is useful for timeouts for which the exact time
+ * of firing does not matter too much, as long as they don't fire too
+ * early.
+ */
+unsigned long __round_jiffies_up_relative(unsigned long j, int cpu)
+{
+	unsigned long j0 = jiffies;
+
+	/* Use j0 because jiffies might change while we run */
+	return round_jiffies_common(j + j0, cpu, true) - j0;
+}
+EXPORT_SYMBOL_GPL(__round_jiffies_up_relative);
+
+/**
+ * round_jiffies_up - function to round jiffies up to a full second
+ * @j: the time in (absolute) jiffies that should be rounded
+ *
+ * This is the same as round_jiffies() except that it will never
+ * round down.  This is useful for timeouts for which the exact time
+ * of firing does not matter too much, as long as they don't fire too
+ * early.
+ */
+unsigned long round_jiffies_up(unsigned long j)
+{
+	return round_jiffies_common(j, raw_smp_processor_id(), true);
+}
+EXPORT_SYMBOL_GPL(round_jiffies_up);
+
+/**
+ * round_jiffies_up_relative - function to round jiffies up to a full second
+ * @j: the time in (relative) jiffies that should be rounded
+ *
+ * This is the same as round_jiffies_relative() except that it will never
+ * round down.  This is useful for timeouts for which the exact time
+ * of firing does not matter too much, as long as they don't fire too
+ * early.
+ */
+unsigned long round_jiffies_up_relative(unsigned long j)
+{
+	return __round_jiffies_up_relative(j, raw_smp_processor_id());
+}
+EXPORT_SYMBOL_GPL(round_jiffies_up_relative);
+
 static inline void set_running_timer(tvec_base_t *base,
 					struct timer_list *timer)
 {