From 420f8f68c9c5148dddf946bebdbc7eacde2172cb Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Sat, 5 Nov 2005 17:25:54 +0100 Subject: [PATCH] x86_64: New heuristics to find out hotpluggable CPUs. With a NR_CPUS==128 kernel with CPU hotplug enabled we would waste 4MB on per CPU data of all possible CPUs. The reason was that HOTPLUG always set up possible map to NR_CPUS cpus and then we need to allocate that much (each per CPU data is roughly ~32k now) The underlying problem is that ACPI didn't tell us how many hotplug CPUs the platform supports. So the old code just assumed all, which would lead to this memory wastage. This implements some new heuristics: - If the BIOS specified disabled CPUs in the ACPI/mptables assume they can be enabled later (this is bending the ACPI specification a bit, but seems like a obvious extension) - The user can overwrite it with a new additionals_cpus=NUM option - Otherwise use half of the available CPUs or 2, whatever is more. Cc: ashok.raj@intel.com Cc: len.brown@intel.com Signed-off-by: Andi Kleen Signed-off-by: Linus Torvalds --- Documentation/x86_64/boot-options.txt | 3 +++ 1 file changed, 3 insertions(+) (limited to 'Documentation') diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt index ffe1c06..a831396 100644 --- a/Documentation/x86_64/boot-options.txt +++ b/Documentation/x86_64/boot-options.txt @@ -122,6 +122,9 @@ SMP cpumask=MASK only use cpus with bits set in mask + additional_cpus=NUM Allow NUM more CPUs for hotplug + (defaults are specified by the BIOS or half the available CPUs) + NUMA numa=off Only set up a single NUMA node spanning all memory. -- cgit v1.1