Performance degredation with latest scheduler code

From: Martin J. Bligh
Date: Thu Jun 10 2004 - 17:58:10 EST

Something messed with the sched peformance between the last copy I picked
up (2.6.5_rc3_mm1) and the stuff that got checked into mainline. I lose
about 17% througput on SDET at high loads, though it's slightly better at
VERY low loads (less processes than nodes). (OK, I'm kind of *assuming*
it's the scheduler, though that seems like by far the most obvious candidate)

Kernbench is worse at lower loads (processes ~= 2x CPUs)

Kernbench: (make -j N vmlinux, where N = 2 x num_cpus)
Elapsed System User CPU
2.6.6-rc3-mjb3 44.90 79.80 586.18 1483.67
2.6.7-rc1-mjb1 45.34 101.04 574.67 1489.00

But actually a bit better at very high loads ...

Kernbench: (make -j vmlinux, maximal tasks)
Elapsed System User CPU
2.6.6-rc3-mjb3 45.56 91.59 590.72 1497.67
2.6.7-rc1-mjb1 44.24 89.98 574.73 1503.33

Diffprofile for kernbench (lower load)

14605 11.2% total
6027 154.2% __copy_from_user_ll
2908 64.8% __copy_to_user_ll
2148 241.6% finish_task_switch
1441 248.0% __wake_up
...
-1714 -3.4% default_idle
-1962 -11.5% do_anonymous_page

What the hell happened there? I'd guess it's the balance on wake stuff,
but removing it doesn't seem to help ... this was the part of the diff
I did to try to revert stuff, which didn't help:



--- 2.6.7-rc1/include/linux/sched.h 2004-05-27 16:22:38.000000000 -0700
+++ 2.6.7-rc1-fixsched/include/linux/sched.h 2004-06-10 09:43:03.000000000 -0700
@@ -630,10 +630,7 @@ struct sched_domain {
.cache_nice_tries = 1, \
.per_cpu_gain = 100, \
.flags = SD_BALANCE_NEWIDLE \
- | SD_BALANCE_EXEC \
- | SD_BALANCE_CLONE \
- | SD_WAKE_AFFINE \
- | SD_WAKE_BALANCE, \
+ | SD_WAKE_AFFINE, \
.last_balance = jiffies, \
.balance_interval = 1, \
.nr_balance_failed = 0, \
@@ -646,15 +643,13 @@ struct sched_domain {
.parent = NULL, \
.groups = NULL, \
.min_interval = 8, \
- .max_interval = 32, \
+ .max_interval = 256*fls(num_online_cpus()),\
.busy_factor = 32, \
.imbalance_pct = 125, \
.cache_hot_time = (10*1000000), \
.cache_nice_tries = 1, \
.per_cpu_gain = 100, \
- .flags = SD_BALANCE_EXEC \
- | SD_BALANCE_CLONE \
- | SD_WAKE_BALANCE, \
+ .flags = SD_BALANCE_EXEC, \
.last_balance = jiffies, \
.balance_interval = 1, \
.nr_balance_failed = 0, \

-
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