linux-kernel - Re: [PATCH] x86/cacheinfo: Define per-CPU num_cache

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Message-ID: <2b1b5ded-522f-1fcf-6daa-354796bedb74@intel.com>
Date:   Mon, 20 Mar 2023 09:44:04 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        x86@...nel.org
Cc:     Ricardo Neri <ricardo.neri@...el.com>,
        linux-kernel@...r.kernel.org,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <len.brown@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Zhang Rui <rui.zhang@...el.com>, Chen Yu <yu.c.chen@...el.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] x86/cacheinfo: Define per-CPU num_cache_leaves

On 3/14/23 16:16, Ricardo Neri wrote:
> -static unsigned short num_cache_leaves;
> +static DEFINE_PER_CPU(unsigned short, num_cache_leaves);
> +
> +static inline unsigned short get_num_cache_leaves(unsigned int cpu)
> +{
> +	return per_cpu(num_cache_leaves, cpu);
> +}

I know it's in generic code, but we do already have this:

static DEFINE_PER_CPU(struct cpu_cacheinfo, ci_cpu_cacheinfo);

which has a num_leaves in it:

struct cpu_cacheinfo {
        struct cacheinfo *info_list;
        unsigned int num_levels;
        unsigned int num_leaves;
        bool cpu_map_populated;
};

That's currently _populated_ from the arch code that you are modifying.
Do we really need this data stored identically in two different per-cpu
locations?

I'd also love to hear some more background on "Intel Meteor Lake" and
_why_ it has an asymmetric cache topology.