linux-kernel - Re: [PATCH v2 4/6] powerpc/smp: Disable MC domain for shared processor

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Message-ID: <87pm1b5ia7.fsf@mail.lhotse>
Date:   Thu, 19 Oct 2023 15:48:48 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Nicholas Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rohan McLure <rmclure@...ux.ibm.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] powerpc/smp: Disable MC domain for shared processor

Srikar Dronamraju <srikar@...ux.vnet.ibm.com> writes:
> Like L2-cache info, coregroup information which is used to determine MC
> sched domains is only present on dedicated LPARs. i.e PowerVM doesn't
> export coregroup information for shared processor LPARs. Hence disable
> creating MC domains on shared LPAR Systems.
>
> Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> ---
>  arch/powerpc/kernel/smp.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index 498c2d51fc20..29da9262cb17 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -1046,6 +1046,10 @@ static struct cpumask *cpu_coregroup_mask(int cpu)
>  
>  static bool has_coregroup_support(void)
>  {
> +	/* Coregroup identification not available on shared systems */
> +	if (is_shared_processor())
> +		return 0;

That will catch guests running under KVM too right? Do we want that?

>  	return coregroup_enabled;

What does coregroup_enabled mean now?

I'd rather this was actually checking the presence of something, rather
than just hard coding that shared processor means no coregroup support.

cheers