Ashok Raj <[email protected]> wrote:
>
> >
> > Does the ACPI problem which you describe occur with present-CPUs,
> > or only with possible-but-not-present ones?
>
> Describing present cpus is not problem.
>
> Only knowing possible-but-not-present upfront is an issue.
>
> logical-cpu-hotplug only: cpu_present_map == cpu_possible_map always
> physical-cpu-hotplug: At boot, cpu_present_map is a subset of possible_map.
>
> Think its best to NOT set cpu_present_map to MASK_ALL as its being proposed,
> but let the arch/platform code figure out early enough to set possible_map
> accurately for that platform. If a platform has no way to determine it,
> then it could use cmdline like what x86_64 introduced (additional_cpus=)
> to overcome that.
There is no proposal to change cpu_present_map.
The problem is cpu_possible_map. That is presently being initialised to
CPU_MASK_ALL, which adversely affects perfoermance. An NR_CPUS=16 kernel
on a 2-way presently has cpu_possible_map=0xffff, which will hurt.
The proposal is this:
From: Andrew Morton <[email protected]>
Initialising cpu_possible_map to all-ones with CONFIG_HOTPLUG_CPU means that
a) All for_each_cpu() loops will iterate across all NR_CPUS CPUs, rather
than over possible ones. That can be quite expensive.
b) Soon we'll be allocating per-cpu areas only for possible CPUs. So with
CPU_MASK_ALL, we'll be wasting memory.
I also switched voyager over to not use CPU_MASK_ALL in the non-CPU-hotplug
case. Will that break it?
I note that parisc is also using CPU_MASK_ALL. Suggest that it stop doing
that.
Cc: James Bottomley <[email protected]>
Cc: Kyle McMartin <[email protected]>
Cc: Paul Jackson <[email protected]>
Cc: Ashok Raj <[email protected]>
Cc: Zwane Mwaikambo <[email protected]>
Cc: Paul Jackson <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
arch/i386/kernel/smpboot.c | 4 ----
arch/i386/mach-voyager/voyager_smp.c | 2 +-
2 files changed, 1 insertion(+), 5 deletions(-)
diff -puN arch/i386/kernel/smpboot.c~x86-dont-initialise-cpu_possible_map-to-all-ones arch/i386/kernel/smpboot.c
--- devel/arch/i386/kernel/smpboot.c~x86-dont-initialise-cpu_possible_map-to-all-ones 2006-02-09 01:11:55.000000000 -0800
+++ devel-akpm/arch/i386/kernel/smpboot.c 2006-02-09 01:12:24.000000000 -0800
@@ -87,11 +87,7 @@ EXPORT_SYMBOL(cpu_online_map);
cpumask_t cpu_callin_map;
cpumask_t cpu_callout_map;
EXPORT_SYMBOL(cpu_callout_map);
-#ifdef CONFIG_HOTPLUG_CPU
-cpumask_t cpu_possible_map = CPU_MASK_ALL;
-#else
cpumask_t cpu_possible_map;
-#endif
EXPORT_SYMBOL(cpu_possible_map);
static cpumask_t smp_commenced_mask;
diff -puN arch/i386/mach-voyager/voyager_smp.c~x86-dont-initialise-cpu_possible_map-to-all-ones arch/i386/mach-voyager/voyager_smp.c
--- devel/arch/i386/mach-voyager/voyager_smp.c~x86-dont-initialise-cpu_possible_map-to-all-ones 2006-02-09 01:11:55.000000000 -0800
+++ devel-akpm/arch/i386/mach-voyager/voyager_smp.c 2006-02-09 01:12:43.000000000 -0800
@@ -240,7 +240,7 @@ static cpumask_t smp_commenced_mask = CP
cpumask_t cpu_callin_map = CPU_MASK_NONE;
cpumask_t cpu_callout_map = CPU_MASK_NONE;
EXPORT_SYMBOL(cpu_callout_map);
-cpumask_t cpu_possible_map = CPU_MASK_ALL;
+cpumask_t cpu_possible_map = CPU_MASK_NONE;
EXPORT_SYMBOL(cpu_possible_map);
/* The per processor IRQ masks (these are usually kept in sync) */
_
-
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