[PATCH] Lengthen and align background timers to decrease wakeups

[Josh Triplett]

This patch changes a few background timers in the Linux kernel to
1) be aligned to full seconds so that multiple timers get handled in one
   processor wakeup
2) have longer timeouts for those timers that can use such longer timeouts

Some of these are a bit crude, but it's effective.

Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
[Josh: Updates for 2.6.22-rc1]
Signed-off-by: Josh Triplett <josh@xxxxxxxxxx>
---
 kernel/time/clocksource.c |   10 ++++++++--
 mm/page-writeback.c       |    8 ++++----
 mm/slab.c                 |    6 +++---
 net/core/neighbour.c      |    4 ++--
 4 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 3db5c3c..77308c4 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -79,11 +79,17 @@ static int watchdog_resumed;
 /*
  * Interval: 0.5sec Threshold: 0.0625s
  */
-#define WATCHDOG_INTERVAL (HZ >> 1)
+#define WATCHDOG_INTERVAL (HZ*10)
 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
 
+static int secondtime;
+
 static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
 {
+	if (!secondtime) {
+		secondtime = 1;
+		return;
+	};
 	if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
 		return;
 
@@ -145,7 +151,7 @@ static void clocksource_watchdog(unsigned long data)
 
 	if (!list_empty(&watchdog_list)) {
 		__mod_timer(&watchdog_timer,
-			    watchdog_timer.expires + WATCHDOG_INTERVAL);
+			    round_jiffies(watchdog_timer.expires + WATCHDOG_INTERVAL));
 	}
 	spin_unlock(&watchdog_lock);
 }
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index eec1481..26318e5 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -77,7 +77,7 @@ int vm_dirty_ratio = 10;
 /*
  * The interval between `kupdate'-style writebacks, in jiffies
  */
-int dirty_writeback_interval = 5 * HZ;
+int dirty_writeback_interval = 15 * HZ;
 
 /*
  * The longest number of jiffies for which data is allowed to remain dirty
@@ -450,7 +450,7 @@ static void wb_kupdate(unsigned long arg)
 
 	oldest_jif = jiffies - dirty_expire_interval;
 	start_jif = jiffies;
-	next_jif = start_jif + dirty_writeback_interval;
+	next_jif = round_jiffies(start_jif + dirty_writeback_interval);
 	nr_to_write = global_page_state(NR_FILE_DIRTY) +
 			global_page_state(NR_UNSTABLE_NFS) +
 			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
@@ -467,7 +467,7 @@ static void wb_kupdate(unsigned long arg)
 		nr_to_write -= MAX_WRITEBACK_PAGES - wbc.nr_to_write;
 	}
 	if (time_before(next_jif, jiffies + HZ))
-		next_jif = jiffies + HZ;
+		next_jif = round_jiffies(jiffies + HZ);
 	if (dirty_writeback_interval)
 		mod_timer(&wb_timer, next_jif);
 }
@@ -491,7 +491,7 @@ int dirty_writeback_centisecs_handler(ctl_table *table, int write,
 static void wb_timer_fn(unsigned long unused)
 {
 	if (pdflush_operation(wb_kupdate, 0) < 0)
-		mod_timer(&wb_timer, jiffies + HZ); /* delay 1 second */
+		mod_timer(&wb_timer, round_jiffies(jiffies + HZ)); /* delay 1 second */
 }
 
 static void laptop_flush(unsigned long unused)
diff --git a/mm/slab.c b/mm/slab.c
index 944b205..6003eef 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -467,8 +467,8 @@ struct kmem_cache {
  * OTOH the cpuarrays can contain lots of objects,
  * which could lock up otherwise freeable slabs.
  */
-#define REAPTIMEOUT_CPUC	(2*HZ)
-#define REAPTIMEOUT_LIST3	(4*HZ)
+#define REAPTIMEOUT_CPUC	(12*HZ)
+#define REAPTIMEOUT_LIST3	(20*HZ)
 
 #if STATS
 #define	STATS_INC_ACTIVE(x)	((x)->num_active++)
@@ -959,7 +959,7 @@ static void __devinit start_cpu_timer(int cpu)
 		init_reap_node(cpu);
 		INIT_DELAYED_WORK(reap_work, cache_reap);
 		schedule_delayed_work_on(cpu, reap_work,
-					__round_jiffies_relative(HZ, cpu));
+					__round_jiffies_relative(HZ*4, cpu));
 	}
 }
 
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 6f3bb73..e6aaa9c 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -696,10 +696,10 @@ next_elt:
 	if (!expire)
 		expire = 1;
 
-	if (expire>HZ)
+	if (expire>4*HZ)
 		mod_timer(&tbl->gc_timer, round_jiffies(now + expire));
 	else
-		mod_timer(&tbl->gc_timer, now + expire);
+		mod_timer(&tbl->gc_timer, round_jiffies(now + 4*HZ));
 
 	write_unlock(&tbl->lock);
 }
-- 
1.5.2-rc2.GIT

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