The patch titled
Optimize calc_load()
has been added to the -mm tree. Its filename is
optimize-calc_load.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: Optimize calc_load()
From: Eric Dumazet <dada1@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: "Siddha, Suresh B" <suresh.b.siddha@xxxxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
kernel/timer.c | 14 +++++++++-----
1 files changed, 9 insertions(+), 5 deletions(-)
diff -puN kernel/timer.c~optimize-calc_load kernel/timer.c
--- a/kernel/timer.c~optimize-calc_load
+++ a/kernel/timer.c
@@ -1146,11 +1146,15 @@ 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);
}
}
_
Patches currently in -mm which might be from dada1@xxxxxxxxxxxxx are
origin.patch
convert-i386-pda-code-to-use-%fs.patch
convert-i386-pda-code-to-use-%fs-fixes.patch
get-rid-of-arch_have_xtime_lock.patch
slab-use-a-multiply-instead-of-a-divide-in-obj_to_index.patch
slab-use-a-multiply-instead-of-a-divide-in-obj_to_index-tweaks.patch
optimize-calc_load.patch
-
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