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| author | Nick Piggin <npiggin@suse.de> | 2007-02-12 00:53:51 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-02-12 09:48:37 -0800 |
| commit | ff91691bccdb741efb2df0489058a4961fa79598 (patch) | |
| tree | eeef6ce3d48df86a7b2c1178a9ba54210b8b8981 /kernel | |
| parent | 0a9ac38246b11892ad20a1eb9deb67adf8c0db2f (diff) | |
| download | lwn-ff91691bccdb741efb2df0489058a4961fa79598.tar.gz lwn-ff91691bccdb741efb2df0489058a4961fa79598.zip | |
[PATCH] sched: avoid div in rebalance_tick
Avoid expensive integer divide 3 times per CPU per tick.
A userspace test of this loop went from 26ns, down to 19ns on a G5; and
from 123ns down to 28ns on a P3.
(Also avoid a variable bit shift, as suggested by Alan. The effect
of this wasn't noticable on the CPUs I tested with).
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched.c | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/kernel/sched.c b/kernel/sched.c index 1fd67e16cd31..08f86178aa34 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2897,14 +2897,16 @@ static void active_load_balance(struct rq *busiest_rq, int busiest_cpu) static void update_load(struct rq *this_rq) { unsigned long this_load; - int i, scale; + unsigned int i, scale; this_load = this_rq->raw_weighted_load; /* Update our load: */ - for (i = 0, scale = 1; i < 3; i++, scale <<= 1) { + for (i = 0, scale = 1; i < 3; i++, scale += scale) { unsigned long old_load, new_load; + /* scale is effectively 1 << i now, and >> i divides by scale */ + old_load = this_rq->cpu_load[i]; new_load = this_load; /* @@ -2914,7 +2916,7 @@ static void update_load(struct rq *this_rq) */ if (new_load > old_load) new_load += scale-1; - this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) / scale; + this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i; } } |