linux-kernel - Re: [PATCH v4 10/10] powerpc/smp: Implement cpu_to_coregroup

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Date:   Fri, 31 Jul 2020 18:02:21 +1000
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>,
        LKML <linux-kernel@...r.kernel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Anton Blanchard <anton@...abs.org>,
        Oliver O'Halloran <oohall@...il.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Michael Neuling <mikey@...ling.org>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Jordan Niethe <jniethe5@...il.com>
Subject: Re: [PATCH v4 10/10] powerpc/smp: Implement cpu_to_coregroup_id

Srikar Dronamraju <srikar@...ux.vnet.ibm.com> writes:
> Lookup the coregroup id from the associativity array.

It's slightly strange that this is called in patch 9, but only properly
implemented here in patch 10.

I'm not saying you have to squash them together, but it would be good if
the change log for patch 9 mentioned that a subsequent commit will
complete the implementation and how that affects the behaviour.

cheers

> If unable to detect the coregroup id, fallback on the core id.
> This way, ensure sched_domain degenerates and an extra sched domain is
> not created.
>
> Ideally this function should have been implemented in
> arch/powerpc/kernel/smp.c. However if its implemented in mm/numa.c, we
> don't need to find the primary domain again.
>
> If the device-tree mentions more than one coregroup, then kernel
> implements only the last or the smallest coregroup, which currently
> corresponds to the penultimate domain in the device-tree.
>
> Cc: linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
> Cc: LKML <linux-kernel@...r.kernel.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Anton Blanchard <anton@...abs.org>
> Cc: Oliver O'Halloran <oohall@...il.com>
> Cc: Nathan Lynch <nathanl@...ux.ibm.com>
> Cc: Michael Neuling <mikey@...ling.org>
> Cc: Gautham R Shenoy <ego@...ux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Valentin Schneider <valentin.schneider@....com>
> Cc: Jordan Niethe <jniethe5@...il.com>
> Reviewed-by : Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
> Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> ---
> Changelog v1 -> v2:
> 	Move coregroup_enabled before getting associativity (Gautham)
>
>  arch/powerpc/mm/numa.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index 0d57779e7942..8b3b3ec7fcc4 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -1218,6 +1218,26 @@ int find_and_online_cpu_nid(int cpu)
>  
>  int cpu_to_coregroup_id(int cpu)
>  {
> +	__be32 associativity[VPHN_ASSOC_BUFSIZE] = {0};
> +	int index;
> +
> +	if (cpu < 0 || cpu > nr_cpu_ids)
> +		return -1;
> +
> +	if (!coregroup_enabled)
> +		goto out;
> +
> +	if (!firmware_has_feature(FW_FEATURE_VPHN))
> +		goto out;
> +
> +	if (vphn_get_associativity(cpu, associativity))
> +		goto out;
> +
> +	index = of_read_number(associativity, 1);
> +	if (index > min_common_depth + 1)
> +		return of_read_number(&associativity[index - 1], 1);
> +
> +out:
>  	return cpu_to_core_id(cpu);
>  }
>  
> -- 
> 2.17.1