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authorEric Dumazet <dada1@cosmosbay.com>2006-12-13 00:35:45 -0800
committerLinus Torvalds <torvalds@woody.osdl.org>2006-12-13 09:05:55 -0800
commitcd7175edf963a92b2c3cd491d3e34afd357e7284 (patch)
tree72c0445ef456f005e26d04568b5a07e8ed95e084 /kernel/timer.c
parentf988443a84528bd30c2f474efa5e2c511959f19b (diff)
downloadlinux-cd7175edf963a92b2c3cd491d3e34afd357e7284.tar.bz2
[PATCH] Optimize calc_load()
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 <dada1@cosmosbay.com> Cc: Ingo Molnar <mingo@elte.hu> Acked-by: "Siddha, Suresh B" <suresh.b.siddha@intel.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel/timer.c')
-rw-r--r--kernel/timer.c14
1 files changed, 9 insertions, 5 deletions
diff --git a/kernel/timer.c b/kernel/timer.c
index 0256ab443d8a..feddf817baa5 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);
}
}