projects/linux·commit cd7175ed

[PATCH] Optimize calc_load()

cd7175ed · Eric Dumazet <[email protected]> · 2006-12-13 00:35:45 -08:00

calc_load() is called by timer interrupt to update avenrun[].  It currently
calls nr_active() at each timer tick (HZ per second), while the update of
avenrun[] is done only once every 5 seconds.  (LOAD_FREQ=5 Hz)

nr_active() is quite expensive on SMP machines, since it has to sum up
nr_running and nr_uninterruptible of all online CPUS, bringing foreign
dirty cache lines.

This patch is an optimization of calc_load() so that nr_active() is called
only if we need it.

The use of unlikely() is welcome since the condition is true only once every
5*HZ time.

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Ingo Molnar <[email protected]>
Acked-by: "Siddha, Suresh B" <[email protected]>
Cc: Nick Piggin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Commit
cd7175edf963a92b2c3cd491d3e34afd357e7284
Parents
f988443a

Changes

1 files changed · +9 −5

FileStatusAddDelContent
kernel/timer.cmodified+9−5View file

kernel/timer.c

View file
diff --git a/kernel/timer.c b/kernel/timer.c
index 0256ab4..feddf81 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1146,11 +1146,15 @@ static inline void calc_load(unsigned long ticks)
unsigned long active_tasks; /* fixed-point */
static int count = LOAD_FREQ;
- active_tasks = count_active_tasks();
- for (count -= ticks; count < 0; count += LOAD_FREQ) {
- CALC_LOAD(avenrun[0], EXP_1, active_tasks);
- CALC_LOAD(avenrun[1], EXP_5, active_tasks);
- CALC_LOAD(avenrun[2], EXP_15, active_tasks);
+ count -= ticks;
+ if (unlikely(count < 0)) {
+ active_tasks = count_active_tasks();
+ do {
+ CALC_LOAD(avenrun[0], EXP_1, active_tasks);
+ CALC_LOAD(avenrun[1], EXP_5, active_tasks);
+ CALC_LOAD(avenrun[2], EXP_15, active_tasks);
+ count += LOAD_FREQ;
+ } while (count < 0);
}
}