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| author | Eric Dumazet <dada1@cosmosbay.com> | 2006-12-13 00:35:45 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.osdl.org> | 2006-12-13 09:05:55 -0800 |
| commit | cd7175edf963a92b2c3cd491d3e34afd357e7284 (patch) | |
| tree | 72c0445ef456f005e26d04568b5a07e8ed95e084 /kernel | |
| parent | f988443a84528bd30c2f474efa5e2c511959f19b (diff) | |
| download | lwn-cd7175edf963a92b2c3cd491d3e34afd357e7284.tar.gz lwn-cd7175edf963a92b2c3cd491d3e34afd357e7284.zip | |
[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')
| -rw-r--r-- | kernel/timer.c | 14 |
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); } } |