Subject: Re: [PATCH] powerpc/64s: introduce CONFIG_MAXSMP to test very large SMP

From: Michael Ellerman <[email-masked]>
Date: Mon, 08 Nov 2021 16:28:41 +1100

Nicholas Piggin <[email-masked]> writes:
> Similarly to x86, add MAXSMP that should help flush out problems with
> vary large SMP and other values associated with very big systems.
>
> Signed-off-by: Nicholas Piggin <[email-masked]>
> ---
>  arch/powerpc/Kconfig                   | 8 ++++++++
>  arch/powerpc/platforms/Kconfig.cputype | 5 +++--
>  2 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index b8f6185d3998..d585fcfa456f 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -64,6 +64,13 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK
>  config NEED_PER_CPU_PAGE_FIRST_CHUNK
>  	def_bool y if PPC64
>  
> +config MAXSMP
> +	bool "Enable Maximum number of SMP Processors and NUMA Nodes"
> +	depends on SMP && DEBUG_KERNEL && PPC_BOOK3S_64
> +	help
> +	  Enable maximum number of CPUS and NUMA Nodes for this architecture.
> +	  If unsure, say N.

As evidenced by the kernel robot report, I think we need to exclude this
from allyesconfig.

Because our max is 16K, larger than the 8K on x86, we are going to be
constantly hitting stack usage errors in driver code. Getting those
fixed tends to take time, because the driver authors don't see the
warnings when they build for other arches, and because the fixes go via
driver trees.

Making MAXSMP depend on !COMPILE_TEST should do the trick.

cheers