linux-kernel - Re: [PATCH v3 05/10] powerpc/smp: Dont assume l2-cache to be superset of sibling

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Date:   Fri, 24 Jul 2020 12:41:08 +0530
From:   Gautham R Shenoy <ego@...ux.vnet.ibm.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        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 v3 05/10] powerpc/smp: Dont assume l2-cache to be
 superset of sibling


On Thu, Jul 23, 2020 at 02:21:11PM +0530, Srikar Dronamraju wrote:
> Current code assumes that cpumask of cpus sharing a l2-cache mask will
> always be a superset of cpu_sibling_mask.
> 
> Lets stop that assumption. cpu_l2_cache_mask is a superset of
> cpu_sibling_mask if and only if shared_caches is set.
> 
> 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>
> Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

Reviewed-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>

> ---
> Changelog v1 -> v2:
> 	Set cpumask after verifying l2-cache. (Gautham)
> 
>  arch/powerpc/kernel/smp.c | 28 +++++++++++++++-------------
>  1 file changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index da27f6909be1..d997c7411664 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -1194,6 +1194,7 @@ static bool update_mask_by_l2(int cpu, struct cpumask *(*mask_fn)(int))
>  	if (!l2_cache)
>  		return false;
> 
> +	cpumask_set_cpu(cpu, mask_fn(cpu));
>  	for_each_cpu(i, cpu_online_mask) {
>  		/*
>  		 * when updating the marks the current CPU has not been marked
> @@ -1276,29 +1277,30 @@ static void add_cpu_to_masks(int cpu)
>  	 * add it to it's own thread sibling mask.
>  	 */
>  	cpumask_set_cpu(cpu, cpu_sibling_mask(cpu));
> +	cpumask_set_cpu(cpu, cpu_core_mask(cpu));
> 
>  	for (i = first_thread; i < first_thread + threads_per_core; i++)
>  		if (cpu_online(i))
>  			set_cpus_related(i, cpu, cpu_sibling_mask);
> 
>  	add_cpu_to_smallcore_masks(cpu);
> -	/*
> -	 * Copy the thread sibling mask into the cache sibling mask
> -	 * and mark any CPUs that share an L2 with this CPU.
> -	 */
> -	for_each_cpu(i, cpu_sibling_mask(cpu))
> -		set_cpus_related(cpu, i, cpu_l2_cache_mask);
>  	update_mask_by_l2(cpu, cpu_l2_cache_mask);
> 
> -	/*
> -	 * Copy the cache sibling mask into core sibling mask and mark
> -	 * any CPUs on the same chip as this CPU.
> -	 */
> -	for_each_cpu(i, cpu_l2_cache_mask(cpu))
> -		set_cpus_related(cpu, i, cpu_core_mask);
> +	if (pkg_id == -1) {
> +		struct cpumask *(*mask)(int) = cpu_sibling_mask;
> +
> +		/*
> +		 * Copy the sibling mask into core sibling mask and
> +		 * mark any CPUs on the same chip as this CPU.
> +		 */
> +		if (shared_caches)
> +			mask = cpu_l2_cache_mask;
> +
> +		for_each_cpu(i, mask(cpu))
> +			set_cpus_related(cpu, i, cpu_core_mask);
> 
> -	if (pkg_id == -1)
>  		return;
> +	}
> 
>  	for_each_cpu(i, cpu_online_mask)
>  		if (get_physical_package_id(i) == pkg_id)
> -- 
> 2.18.2
>