Use deferable timer in background operations thread,
so that it won't cause unnecessary wakeups. Typically,
wakeups are seen in the range 60ms to 2secs (for HZ=100)
after the thread is scheduled out. In general, during this
delay the processor can go into sleep, if there is no other
activity. Since, the work done in this background operation
is not critical and can be handled as soon as when timer
expires and processor wakes up for other critical events,
we mark the timer responsible for wakeup of this thread
as deferable timer. Otherwise, the processor wakesup
unnecessarily to handle the background operations causing
higher power consumption in idle state.

Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
---
 yaffs_vfs_multi.c  |   18 ++++++++++++------
 yaffs_vfs_single.c |    5 ++---
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/yaffs_vfs_multi.c b/yaffs_vfs_multi.c
index b8e5124..66d7131 100644
--- a/yaffs_vfs_multi.c
+++ b/yaffs_vfs_multi.c
@@ -128,10 +128,17 @@
 #define YPROC_ROOT  NULL
 #endif
 
-#if (LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 26))
-#define Y_INIT_TIMER(a)	init_timer(a)
+#if (LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 15))
+#define Y_INIT_TIMER(a, b, c)		\
+	do {				\
+		(a)->function = b;	\
+		(a)->data = c;		\
+		init_timer(a);		\
+	} while (0)
+#elif (LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 36))
+#define Y_INIT_TIMER(a, b, c)  setup_timer(a, b, c)
 #else
-#define Y_INIT_TIMER(a)	init_timer_on_stack(a)
+#define Y_INIT_TIMER(a, b, c)	setup_deferrable_timer_on_stack(a, b, c)
 #endif
 
 #if (LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 17))
@@ -2300,10 +2307,9 @@ static int yaffs_bg_thread_fn(void *data)
 		if (time_before(expires, now))
 			expires = now + HZ;
 
-		Y_INIT_TIMER(&timer);
+		Y_INIT_TIMER(&timer, yaffs_background_waker,
+				(unsigned long)current);
 		timer.expires = expires + 1;
-		timer.data = (unsigned long)current;
-		timer.function = yaffs_background_waker;
 
 		set_current_state(TASK_INTERRUPTIBLE);
 		add_timer(&timer);
diff --git a/yaffs_vfs_single.c b/yaffs_vfs_single.c
index f822845..1ddc03e 100644
--- a/yaffs_vfs_single.c
+++ b/yaffs_vfs_single.c
@@ -1636,10 +1636,9 @@ static int yaffs_bg_thread_fn(void *data)
 		if (time_before(expires, now))
 			expires = now + HZ;
 
-		init_timer_on_stack(&timer);
+		setup_deferrable_timer_on_stack(&timer, yaffs_background_waker,
+				(unsigned long)current);
 		timer.expires = expires + 1;
-		timer.data = (unsigned long)current;
-		timer.function = yaffs_background_waker;
 
 		set_current_state(TASK_INTERRUPTIBLE);
 		add_timer(&timer);
-- 
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.