Re: [RFC part2 PATCH 2/9] ARM64 / ACPI: Prefill cpu possible/present maps and map logical cpu id to APIC id

Rob Herring
2013-12-04T15:47:52Z

On Tue, Dec 3, 2013 at 10:39 AM, Hanjun Guo <hanjun.guo@linaro.org> wrote:
> When boot the kernel with MADT, the cpu possible and present maps should be
> prefilled for cpu topology and acpi based cpu hot-plug.
>
> The logic cpu id maps to APIC id (GIC id) is also implemented, it is needed
> for acpi processor drivers.
>
> Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
> ---
> arch/arm64/include/asm/acpi.h | 10 ++--
> arch/arm64/kernel/setup.c | 2 +
> arch/arm64/kernel/smp.c | 2 +
> drivers/acpi/plat/arm-core.c | 118 +++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 129 insertions(+), 3 deletions(-)

[snip]

> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index a0c2ca6..1428024 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -420,7 +420,9 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
> if (err)
> continue;
>
> +#ifndef CONFIG_ACPI
> set_cpu_present(cpu, true);
> +#endif

Should this be moved to DT cpu topology related code?

> max_cpus--;
> }
> }
> diff --git a/drivers/acpi/plat/arm-core.c b/drivers/acpi/plat/arm-core.c
> index 45ff625..8527ecc 100644
> --- a/drivers/acpi/plat/arm-core.c
> +++ b/drivers/acpi/plat/arm-core.c

[snip]

> @@ -221,6 +284,61 @@ static int __init acpi_parse_madt_gic_distributor_entries(void)
> return 0;
> }
>
> +static int setup_possible_cpus __initdata = -1;
> +static int __init _setup_possible_cpus(char *str)
> +{
> + get_option(&str, &setup_possible_cpus);
> + return 0;
> +}
> +early_param("possible_cpus", _setup_possible_cpus);

This does not seem ACPI or ARM specific.

> +
> +/*
> + * cpu_possible_mask should be static, it cannot change as cpu's
> + * are onlined, or offlined. The reason is per-cpu data-structures
> + * are allocated by some modules at init time, and dont expect to
> + * do this dynamically on cpu arrival/departure.
> + * cpu_present_mask on the other hand can change dynamically.
> + * In case when cpu_hotplug is not compiled, then we resort to current
> + * behaviour, which is cpu_possible == cpu_present.
> + * - Ashok Raj
> + *
> + * Three ways to find out the number of additional hotplug CPUs:
> + * - If the BIOS specified disabled CPUs in ACPI/mptables use that.
> + * - The user can overwrite it with possible_cpus=NUM
> + * - Otherwise don't reserve additional CPUs.
> + * We do this because additional CPUs waste a lot of memory.
> + * -AK
> + */
> +void __init prefill_possible_map(void)
> +{
> + int i;
> + int possible, disabled_cpus;
> +
> + disabled_cpus = total_cpus - available_cpus;
> +
> + if (setup_possible_cpus == -1) {
> + if (disabled_cpus > 0)
> + setup_possible_cpus = disabled_cpus;
> + else
> + setup_possible_cpus = 0;
> + }
> +
> + possible = available_cpus + setup_possible_cpus;
> +
> + pr_info("SMP: the system is limited to %d CPUs\n", nr_cpu_ids);
> +
> + if (possible > nr_cpu_ids)
> + possible = nr_cpu_ids;
> +
> + pr_info("SMP: Allowing %d CPUs, %d hotplug CPUs\n",
> + possible, max((possible - available_cpus), 0));
> +
> + for (i = 0; i < possible; i++)
> + set_cpu_possible(i, true);
> + for (; i < NR_CPUS; i++)
> + set_cpu_possible(i, false);
> +}

This does not seem ACPI or ARM specific either.

Rob