From cd7175edf963a92b2c3cd491d3e34afd357e7284 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 13 Dec 2006 00:35:45 -0800 Subject: [PATCH] [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 Cc: Ingo Molnar Acked-by: "Siddha, Suresh B" Cc: Nick Piggin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/timer.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/kernel/timer.c b/kernel/timer.c index 0256ab443d8..feddf817baa 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); } } -- 2.20.1