linux-kernel - Re: [PATCH 2/3] powerpc/numa: Populate distance map correctly

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Message-ID: <87im386wuh.mognet@arm.com>
Date:   Mon, 24 May 2021 15:16:22 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        linuxppc-dev@...ts.ozlabs.org,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Cheloha <cheloha@...ux.ibm.com>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Geetika Moolchandani <Geetika.Moolchandani1@....com>
Subject: Re: [PATCH 2/3] powerpc/numa: Populate distance map correctly

On 20/05/21 21:14, Srikar Dronamraju wrote:
> +int arch_populate_distance_map(unsigned long *distance_map)
> +{
> +	int i;
> +	int distance = LOCAL_DISTANCE;
> +
> +	bitmap_set(distance_map, distance, 1);
> +
> +	if (!form1_affinity) {
> +		bitmap_set(distance_map, REMOTE_DISTANCE, 1);
> +		return 0;
> +	}
> +
> +	for (i = 0; i < distance_ref_points_depth; i++) {
> +		distance *= 2;
> +		bitmap_set(distance_map, distance, 1);

Do you have guarantees your distance values will always be in the form of

  LOCAL_DISTANCE * 2^i

because that certainly isn't true for x86/arm64.

> +	}
> +	return 0;
> +}
> +
>  /*
>   * Returns nid in the range [0..nr_node_ids], or -1 if no useful NUMA
>   * info is found.
> --
> 2.27.0