sched domains kernbench improvements

[Nick Piggin <piggin@cyberone.com.au>]

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Con,
I was able to reproduce your half-load kernbench problems
on the non-NUMA stp 8-way.

I made a pretty simple "lessidle" patch which tweaks some
sched domain parameters to be more inclined to move tasks,
especially when idle. That brought performance to nearly
exactly the same as 2.6.3.

Context switches are still up, but user and system time
is down a bit. So indicates it is still less balance-happy
but is obviously enough to bring the idle time down.

2.6.3:                http://khack.osdl.org/stp/288459/
2.6.3-mm4-lessidle:   http://khack.osdl.org/stp/288995/

Phew! So it is more a matter of tuning than anything
fundamental. It may be that the patch now makes balancing
too aggressive, but it is probably better to err on the
side that is closer to 2.6 behaviour.

I haven't tested this on much else.


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 linux-2.6-npiggin/include/linux/sched.h |   16 ++++++++--------
 linux-2.6-npiggin/kernel/sched.c        |    5 +++++
 2 files changed, 13 insertions(+), 8 deletions(-)

diff -puN include/linux/sched.h~sched-lessidle include/linux/sched.h
--- linux-2.6/include/linux/sched.h~sched-lessidle	2004-02-21 10:57:07.000000000 +1100
+++ linux-2.6-npiggin/include/linux/sched.h	2004-02-21 10:59:46.000000000 +1100
@@ -598,11 +598,11 @@ struct sched_domain {
 	.parent			= NULL,			\
 	.groups			= NULL,			\
 	.min_interval		= 1,			\
-	.max_interval		= 8,			\
-	.busy_factor		= 32,			\
+	.max_interval		= 4,			\
+	.busy_factor		= 64,			\
 	.imbalance_pct		= 125,			\
-	.cache_hot_time		= (5*1000000),		\
-	.cache_nice_tries	= 2,			\
+	.cache_hot_time		= (5*1000000/2),	\
+	.cache_nice_tries	= 1,			\
 	.flags			= SD_FLAG_FASTMIGRATE | SD_FLAG_NEWIDLE,\
 	.last_balance		= jiffies,		\
 	.balance_interval	= 1,			\
@@ -615,11 +615,11 @@ struct sched_domain {
 	.span			= CPU_MASK_NONE,	\
 	.parent			= NULL,			\
 	.groups			= NULL,			\
-	.min_interval		= 20,			\
-	.max_interval		= 1000*fls(num_online_cpus()),\
-	.busy_factor		= 4,			\
+	.min_interval		= 8,			\
+	.max_interval		= 256*fls(num_online_cpus()),\
+	.busy_factor		= 8,			\
 	.imbalance_pct		= 125,			\
-	.cache_hot_time		= (5*1000000),		\
+	.cache_hot_time		= (10*1000000),		\
 	.cache_nice_tries	= 1,			\
 	.flags			= SD_FLAG_EXEC,		\
 	.last_balance		= jiffies,		\
diff -puN kernel/sched.c~sched-lessidle kernel/sched.c
--- linux-2.6/kernel/sched.c~sched-lessidle	2004-02-21 10:57:10.000000000 +1100
+++ linux-2.6-npiggin/kernel/sched.c	2004-02-21 16:15:18.000000000 +1100
@@ -1493,6 +1493,11 @@ nextgroup:
 	return busiest;
 
 out_balanced:
+	if (busiest && idle == NEWLY_IDLE) {
+		*imbalance = 1;
+		return busiest;
+	}
+
 	*imbalance = 0;
 	return NULL;
 }

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