Messages in this thread Patch in this message | | | From | Eric Dumazet <> | Subject | [PATCH] Optimize calc_load() | Date | Mon, 11 Dec 2006 14:50:07 +0100 |
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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> --- linux-2.6.19/kernel/timer.c 2006-12-11 12:27:28.000000000 +0100 +++ linux-2.6.19-ed/kernel/timer.c 2006-12-11 12:29:11.000000000 +0100 @@ -1008,11 +1008,15 @@ static inline void calc_load(unsigned lo 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); } } | |