The patch titled
sched: avoid div in rebalance_tick
has been added to the -mm tree. Its filename is
sched-avoid-div-in-rebalance_tick.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: sched: avoid div in rebalance_tick
From: Nick Piggin <npiggin@xxxxxxx>
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@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
kernel/sched.c | 8 +++++---
1 files changed, 5 insertions(+), 3 deletions(-)
diff -puN kernel/sched.c~sched-avoid-div-in-rebalance_tick kernel/sched.c
--- a/kernel/sched.c~sched-avoid-div-in-rebalance_tick
+++ a/kernel/sched.c
@@ -2887,14 +2887,16 @@ static void active_load_balance(struct r
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;
/*
@@ -2904,7 +2906,7 @@ static void update_load(struct rq *this_
*/
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;
}
}
_
Patches currently in -mm which might be from npiggin@xxxxxxx are
git-block.patch
sched-avoid-div-in-rebalance_tick.patch
-
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