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SubjectRe: [PATCH 1/2] powerpc: Detect the presence of big-core with interleaved threads
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"Gautham R. Shenoy" <ego@linux.vnet.ibm.com> writes:

> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> index 0af5c11..884dff2 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -436,8 +438,56 @@ static void __init cpu_init_thread_core_maps(int tpc)
> printk(KERN_DEBUG " (thread shift is %d)\n", threads_shift);
> }
>
> -
> u32 *cpu_to_phys_id = NULL;
> +/*
> + * check_for_interleaved_big_core - Checks if the core represented by
> + * dn is a big-core whose threads are interleavings of the
> + * threads of the component small cores.
> + *
> + * @dn: device node corresponding to the core.
> + *
> + * Returns true if the core is a interleaved big-core.
> + * Returns false otherwise.
> + */
> +static inline bool check_for_interleaved_big_core(struct device_node *dn)
> +{
> + int len, nr_groups, threads_per_group;
> + const __be32 *thread_groups;
> + __be32 *thread_list, *first_cpu_idx;
> + int cur_cpu, next_cpu, i, j;
> +
> + thread_groups = of_get_property(dn, "ibm,thread-groups", &len);
> + if (!thread_groups)
> + return false;

There are better device tree APIs than bare of_get_property() these
days, can you try to use those?

> + nr_groups = be32_to_cpu(*(thread_groups + 1));
> + if (nr_groups <= 1)
> + return false;

eg. this would be of_property_read_u32_index()

> +
> + threads_per_group = be32_to_cpu(*(thread_groups + 2));
> + thread_list = (__be32 *)thread_groups + 3;
> +
> + /*
> + * In case of an interleaved big-core, the thread-ids of the
> + * big-core can be obtained by interleaving the the thread-ids
> + * of the component small
> + *
> + * Eg: On a 8-thread big-core with two SMT4 small cores, the
> + * threads of the two component small cores will be
> + * {0, 2, 4, 6} and {1, 3, 5, 7}.
> + */
> + for (i = 0; i < nr_groups; i++) {
> + first_cpu_idx = thread_list + i * threads_per_group;
> +
> + for (j = 0; j < threads_per_group - 1; j++) {
> + cur_cpu = be32_to_cpu(*(first_cpu_idx + j));
> + next_cpu = be32_to_cpu(*(first_cpu_idx + j + 1));
> + if (next_cpu != cur_cpu + nr_groups)
> + return false;
> + }
> + }
> + return true;
> +}
>
> /**
> * setup_cpu_maps - initialize the following cpu maps:
> @@ -565,7 +615,16 @@ void __init smp_setup_cpu_maps(void)
> vdso_data->processorCount = num_present_cpus();
> #endif /* CONFIG_PPC64 */
>
> - /* Initialize CPU <=> thread mapping/
> + dn = of_find_node_by_type(NULL, "cpu");
> + if (dn) {
> + if (check_for_interleaved_big_core(dn)) {
> + has_interleaved_big_core = true;
> + pr_info("Detected interleaved big-cores\n");
> + }
> + of_node_put(dn);
> + }

This is a bit untidy, given how unlikely it is that you would have no
CPUs :)

You should be able to do the lookup of the property and the setting of
has_interleaved_big_core all inside check_for_interleaved_big_core().

cheers

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