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

Simon Arlott
2007-03-01T18:52:33Z

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@fire.lp0.eu>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
---
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