Re: [PATCH v3] x86/cpu: Allow higher NR_CPUS values

From: Ingo Molnar
Date: Thu Nov 07 2013 - 04:16:09 EST



* Josh Boyer <jwboyer@xxxxxxxxxx> wrote:

> The current range for SMP configs is 2 - 512 CPUs, or a full 4096 in the
> case of MAXSMP. There are machines that have 1024 CPUs in them today
> and configuring a kernel for that means you are forced to set MAXSMP.
> This adds additional unnecessary overhead. While that overhead might be
> considered tiny for large machines, it isn't necessarily so if you are
> building a kernel that runs across a wide variety of machines.
>
> To cover the range of more common machines today, we allow NR_CPUS to be
> up to 4096 when CPUMASK_OFFSTACK is enabled. Relatedly, we no longer make
> that option depend on DEBUG_PER_CPU_MASKS.

> index b3c8be0..50b47cd 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -342,7 +342,8 @@ config CHECK_SIGNATURE
> bool
>
> config CPUMASK_OFFSTACK
> - bool "Force CPU masks off stack" if DEBUG_PER_CPU_MAPS
> + bool "Force CPU masks off stack"
> + depends on SMP
> help
> Use dynamic allocation for cpumask_var_t, instead of putting
> them on the stack. This is a bit more expensive, but avoids

So this chunk really doesn't belong into the patch - it should be a
separate patch.

Also, because I already applied the patch (sans the unrelated chunk)
please only send this single change against tip:master.

Thanks,

Ingo
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