linux-kernel - Re: [PATCH v2 09/10] Powerpc/smp: Create coregroup domain

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Date:   Wed, 22 Jul 2020 12:34:36 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <michaele@....ibm.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Nick Piggin <npiggin@....ibm.com>,
        Oliver OHalloran <oliveroh@....ibm.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Michael Neuling <mikey@...ux.ibm.com>,
        Anton Blanchard <anton@....ibm.com>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.ibm.com>,
        Jordan Niethe <jniethe5@...il.com>
Subject: Re: [PATCH v2 09/10] Powerpc/smp: Create coregroup domain

Hi Srikar,

On Tue, Jul 21, 2020 at 05:08:13PM +0530, Srikar Dronamraju wrote:
> Add percpu coregroup maps and masks to create coregroup domain.
> If a coregroup doesn't exist, the coregroup domain will be degenerated
> in favour of SMT/CACHE domain.
> 
> Cc: linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
> Cc: LKML <linux-kernel@...r.kernel.org>
> Cc: Michael Ellerman <michaele@....ibm.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Valentin Schneider <valentin.schneider@....com>
> Cc: Nick Piggin <npiggin@....ibm.com>
> Cc: Oliver OHalloran <oliveroh@....ibm.com>
> Cc: Nathan Lynch <nathanl@...ux.ibm.com>
> Cc: Michael Neuling <mikey@...ux.ibm.com>
> Cc: Anton Blanchard <anton@....ibm.com>
> Cc: Gautham R Shenoy <ego@...ux.vnet.ibm.com>
> Cc: Vaidyanathan Srinivasan <svaidy@...ux.ibm.com>
> Cc: Jordan Niethe <jniethe5@...il.com>
> Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

A query below.

> ---
> Changelog v1 -> v2:
> Powerpc/smp: Create coregroup domain
> 	Moved coregroup topology fixup to fixup_topology (Gautham)
> 
>  arch/powerpc/include/asm/topology.h | 10 ++++++++
>  arch/powerpc/kernel/smp.c           | 38 +++++++++++++++++++++++++++++
>  arch/powerpc/mm/numa.c              |  5 ++++
>  3 files changed, 53 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
> index f0b6300e7dd3..6609174918ab 100644
> --- a/arch/powerpc/include/asm/topology.h
> +++ b/arch/powerpc/include/asm/topology.h

[..snip..]

> @@ -91,6 +92,7 @@ enum {
>  	smt_idx,
>  #endif
>  	bigcore_idx,
> +	mc_idx,
>  	die_idx,
>  };
> 


[..snip..]

> @@ -879,6 +896,7 @@ static struct sched_domain_topology_level powerpc_topology[] = {
>  	{ cpu_smt_mask, powerpc_smt_flags, SD_INIT_NAME(SMT) },
>  #endif
>  	{ cpu_bigcore_mask, SD_INIT_NAME(BIGCORE) },
> +	{ cpu_mc_mask, SD_INIT_NAME(MC) },
>  	{ cpu_cpu_mask, SD_INIT_NAME(DIE) },
>  	{ NULL, },
>  };


[..snip..]

> @@ -1386,6 +1421,9 @@ int setup_profiling_timer(unsigned int multiplier)
> 
>  static void fixup_topology(void)
>  {
> +	if (!has_coregroup_support())
> +		powerpc_topology[mc_idx].mask = cpu_bigcore_mask;
> +

Shouldn't we move this condition after doing the fixup for shared
caches ? Because if we have shared_caches, but not core_group, then we
want the coregroup domain to degenerate correctly.


>  	if (shared_caches) {
>  		pr_info("Using shared cache scheduler topology\n");
>  		powerpc_topology[bigcore_idx].mask = shared_cache_mask;


--
Thanks and regards
gautham.