On Tue, Nov 19, 2013 at 11:09 AM, Ingo Molnar <mi...@kernel.org> wrote:
>
> As you pointed out offstack is definitely nonsensical for
> NR_CPUS <= 64. (on 64-bit CPUs) On-stack is known to crash with
> NR_CPUS >= 1024.
>
> The 128..512 CPUs range is somewhat of an unknown.
Agreed. And we could even decide to ask somewhere in that range.
I think 128 bits is still safely "don't bother with an external
pointer" (it's just two words, it's like a "struct list_head" -
there's no way that should be unsafe on the stack). Once we get to 256
bits I start going "Hmm, that's 32 bytes, maybe an external allocation
makes sense..."
I'd personally put the cut-off point at just keeping it on-stack if
it's smaller than or equal to 256. But I agree that at that point it's
really just a judgement call.
Linus
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