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@linux.intel.com>

diff -purN linux-2.6.20/kernel/time/clocksource.c linux-2.6.21-rc5/kernel/time/clocksource.c
--- linux-2.6.20/kernel/time/clocksource.c	2007-05-10 12:16:30.000000000 -0400
+++ linux-2.6.21-rc5/kernel/time/clocksource.c	2007-04-09 09:58:57.000000000 -0400
@@ -77,11 +77,17 @@ static cycle_t watchdog_last;
 /*
  * Interval: 0.5sec Treshold: 0.0625s
  */
-#define WATCHDOG_INTERVAL (HZ >> 1)
+#define WATCHDOG_INTERVAL (HZ*10)
 #define WATCHDOG_TRESHOLD (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_TRESHOLD && delta < WATCHDOG_TRESHOLD)
 		return;
 
@@ -132,7 +138,7 @@ static void clocksource_watchdog(unsigne
 
 	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 -purN linux-2.6.20/mm/page-writeback.c linux-2.6.21-rc5/mm/page-writeback.c
--- linux-2.6.20/mm/page-writeback.c	2007-05-10 12:16:30.000000000 -0400
+++ linux-2.6.21-rc5/mm/page-writeback.c	2007-04-10 11:29:38.000000000 -0400
@@ -77,7 +77,7 @@ int vm_dirty_ratio = 40;
 /*
  * 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
@@ -420,7 +420,7 @@ 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);
@@ -437,7 +437,7 @@ 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);
 }
@@ -461,7 +461,7 @@ int dirty_writeback_centisecs_handler(ct
 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 -purN linux-2.6.20/mm/slab.c linux-2.6.21-rc5/mm/slab.c
--- linux-2.6.20/mm/slab.c	2007-05-10 12:16:30.000000000 -0400
+++ linux-2.6.21-rc5/mm/slab.c	2007-04-16 09:49:55.000000000 -0400
@@ -457,8 +457,8 @@ 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++)
@@ -958,7 +958,7 @@ static void __devinit start_cpu_timer(in
 		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 -purN linux-2.6.20/net/core/neighbour.c linux-2.6.21-rc5/net/core/neighbour.c
--- linux-2.6.20/net/core/neighbour.c	2007-05-10 12:16:35.000000000 -0400
+++ linux-2.6.21-rc5/net/core/neighbour.c	2007-04-16 09:50:28.000000000 -0400
@@ -693,10 +693,10 @@ 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);
 }