Messages in this thread Patch in this message | | | Date | Thu, 23 Nov 2023 19:33:08 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH ARM64]: Introduce CONFIG_MAXSMP to allow up to 512 cpus |
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On Mon, Nov 20, 2023 at 05:04:35PM -0800, Christoph Lameter (Ampere) wrote: > Index: linux/arch/arm64/Kconfig > =================================================================== > --- linux.orig/arch/arm64/Kconfig > +++ linux/arch/arm64/Kconfig > @@ -1402,10 +1402,56 @@ config SCHED_SMT > MultiThreading at a cost of slightly increased overhead in some > places. If unsure say N here. > > + > +config MAXSMP > + bool "Compile kernel with support for the maximum number of SMP Processors" > + depends on SMP && DEBUG_KERNEL > + select CPUMASK_OFFSTACK > + help > + Enable maximum number of CPUS and NUMA Nodes for this architecture. > + If unsure, say N. > + > +# > +# The maximum number of CPUs supported: > +# > +# The main config value is NR_CPUS, which defaults to NR_CPUS_DEFAULT, > +# and which can be configured interactively in the > +# [NR_CPUS_RANGE_BEGIN ... NR_CPUS_RANGE_END] range. > +# > +# ( If MAXSMP is enabled we just use the highest possible value and disable > +# interactive configuration. ) > +# > + > +config NR_CPUS_RANGE_BEGIN > + int > + default NR_CPUS_RANGE_END if MAXSMP > + default 1 if !SMP > + default 2
We don't support !SMP on arm64.
> + > +config NR_CPUS_RANGE_END > + int > + default 8192 if SMP && CPUMASK_OFFSTACK > + default 512 if SMP && !CPUMASK_OFFSTACK > + default 1 if !SMP > + > +config NR_CPUS_DEFAULT > + int > + default 512 if MAXSMP > + default 64 if SMP > + default 1 if !SMP > + > config NR_CPUS > - int "Maximum number of CPUs (2-4096)" > - range 2 4096 > - default "256" > + int "Set maximum number of CPUs" if SMP && !MAXSMP > + range NR_CPUS_RANGE_BEGIN NR_CPUS_RANGE_END > + default NR_CPUS_DEFAULT > + help > + This allows you to specify the maximum number of CPUs which this > + kernel will support. If CPUMASK_OFFSTACK is enabled, the maximum > + supported value is 8192, otherwise the maximum value is 512. The > + minimum value which makes sense is 2. > + > + This is purely to save memory: each supported CPU adds about 8KB > + to the kernel image.
Is this all needed just to select CPUMASK_OFFSTACK if larger NR_CPUS? Would something like this do:
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 7b071a00425d..697d5700bad1 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -119,6 +119,7 @@ config ARM64 select CLONE_BACKWARDS select COMMON_CLK select CPU_PM if (SUSPEND || CPU_IDLE) + select CPUMASK_OFFSTACK if NR_CPUS > 512 select CRC32 select DCACHE_WORD_ACCESS select DYNAMIC_FTRACE if FUNCTION_TRACER togehther with a larger NR_CPUS in defconfig?
-- Catalin
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