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Date: Thu, 15 Apr 2021 22:41:34 +0530
From: Gautham R Shenoy <ego@linux.vnet.ibm.com>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Subject: Re: [PATCH 1/3] powerpc/smp: Reintroduce cpu_core_mask
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Cc: Nathan Lynch <nathanl@linux.ibm.com>,
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

Hi Srikar,

On Thu, Apr 15, 2021 at 05:39:32PM +0530, Srikar Dronamraju wrote:
 [..snip..]



> @@ -1485,12 +1486,36 @@ static void add_cpu_to_masks(int cpu)
>  	add_cpu_to_smallcore_masks(cpu);
> 
>  	/* In CPU-hotplug path, hence use GFP_ATOMIC */
> -	alloc_cpumask_var_node(&mask, GFP_ATOMIC, cpu_to_node(cpu));
> +	ret = alloc_cpumask_var_node(&mask, GFP_ATOMIC, cpu_to_node(cpu));
>  	update_mask_by_l2(cpu, &mask);
> 
>  	if (has_coregroup_support())
>  		update_coregroup_mask(cpu, &mask);
> 
> +	if (chip_id == -1 || !ret) {
> +		cpumask_copy(per_cpu(cpu_core_map, cpu), cpu_cpu_mask(cpu));
> +		goto out;
> +	}
> +
> +	if (shared_caches)
> +		submask_fn = cpu_l2_cache_mask;
> +
> +	/* Update core_mask with all the CPUs that are part of submask */
> +	or_cpumasks_related(cpu, cpu, submask_fn, cpu_core_mask);
>

If coregroups exist, we can add the cpus of the coregroup to the
cpu_core_mask thereby reducing the scope of the for_each_cpu() search
below. This will still cut down the time on Baremetal systems
supporting coregroups.


> +	/* Skip all CPUs already part of current CPU core mask */
> +	cpumask_andnot(mask, cpu_online_mask, cpu_core_mask(cpu));
> +
> +	for_each_cpu(i, mask) {
> +		if (chip_id == cpu_to_chip_id(i)) {
> +			or_cpumasks_related(cpu, i, submask_fn, cpu_core_mask);
> +			cpumask_andnot(mask, mask, submask_fn(i));
> +		} else {
> +			cpumask_andnot(mask, mask, cpu_core_mask(i));
> +		}
> +	}
> +
> +out:
>  	free_cpumask_var(mask);
>  }
> 
> -- 
> 2.25.1
>