Commit 4bbf39c2 authored Feb 17, 2006 by Ingo Molnar Committed by Linus Torvalds Feb 17, 2006

[PATCH] Introduce CONFIG_DEFAULT_MIGRATION_COST



Heiko Carstens <heiko.carstens@de.ibm.com> wrote:

  The boot sequence on s390 sometimes takes ages and we spend a very long
  time (up to one or two minutes) in calibrate_migration_costs.  The time
  spent there differs from boot to boot.  Also the calculated costs differ
  a lot.  I've seen differences by up to a factor of 15 (yes, factor not
  percent).  Also I doubt that making these measurements make much sense on
  a completely virtualized architecture where you cannot tell how much cpu
  time you will get anyway.

So introduce the CONFIG_DEFAULT_MIGRATION_COST method for an architecture
to set the scheduler migration costs.  This turns off automatic detection
of migration costs.  Makes sense on virtual platforms, where migration
costs are hard to measure accurately.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 05efc67d

arch/s390/Kconfig

+4 −0

Original line number	Diff line number	Diff line
		@@ -80,6 +80,10 @@ config HOTPLUG_CPU
		can be controlled through /sys/devices/system/cpu/cpu#.
		Say N if you want to disable CPU hotplug.

		config DEFAULT_MIGRATION_COST
		int
		default "1000000"

		config MATHEMU
		bool "IEEE FPU emulation"
		depends on MARCH_G5

kernel/sched.c

+12 −1

Original line number	Diff line number	Diff line
		@@ -5058,7 +5058,18 @@ static void init_sched_build_groups(struct sched_group groups[], cpumask_t span,
		#define MAX_DOMAIN_DISTANCE 32

		static unsigned long long migration_cost[MAX_DOMAIN_DISTANCE] =
		{ [ 0 ... MAX_DOMAIN_DISTANCE-1 ] = -1LL };
		{ [ 0 ... MAX_DOMAIN_DISTANCE-1 ] =
		/*
		* Architectures may override the migration cost and thus avoid
		* boot-time calibration. Unit is nanoseconds. Mostly useful for
		* virtualized hardware:
		*/
		#ifdef CONFIG_DEFAULT_MIGRATION_COST
		CONFIG_DEFAULT_MIGRATION_COST
		#else
		-1LL
		#endif
		};

		/*
		* Allow override of migration cost - in units of microseconds.

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