[PATCH] timer: Add an initial 0.5s delay to calc_load

[Simon Arlott]

This adds an initial 0.5s delay to calc_load so that it avoids updating 
load at the same time as tasks scheduled using round_jiffies, otherwise 
the load average is badly affected by tasks that run every time calc_load 
does (currently every 5s).

I'm assuming this change doesn't affect the intention of round_jiffies, 
to avoid tasks waking the cpu at different times, because calc_load is 
already run very often by a call from update_times(ticks) on every timer 
interrupt.

Signed-off-by: Simon Arlott <simon@xxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
---
Without this change or an appropriate equivalent, my change to cxacru 
causes the load to stay around 1.00 even when mostly idle since it now 
runs every second using round_jiffies:
> [  332.416288] cxacru_poll_status(..), jiffies=5000 [start]
> [  332.417312] calc_load(1), count=-1, jiffies=5001 [start]
> [  332.417322] calc_load(1), count=4999, jiffies=5001 [finish]
> [  332.423382] cxacru_poll_status(..), jiffies=5007, next=993 [finish]

kernel/timer.c |    2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/timer.c b/kernel/timer.c
index cb1b86a..4bb21b5 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1225,7 +1225,7 @@ EXPORT_SYMBOL(avenrun);
static inline void calc_load(unsigned long ticks)
{
	unsigned long active_tasks; /* fixed-point */
-	static int count = LOAD_FREQ;
+	static int count = LOAD_FREQ + HZ/2;

	count -= ticks;
	if (unlikely(count < 0)) {
--
1.5.0.1


--
Simon Arlott
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