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

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Message-ID: <52A080C8.5080909@linaro.org>
Date:	Thu, 05 Dec 2013 21:34:00 +0800
From:	Hanjun Guo <hanjun.guo@...aro.org>
To:	Rob Herring <robherring2@...il.com>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Linaro Patches <patches@...aro.org>,
	Olof Johansson <olof@...om.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <rob.herring@...xeda.com>,
	linaro-acpi@...ts.linaro.org, linux-acpi@...r.kernel.org,
	Grant Likely <grant.likely@...aro.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC part2 PATCH 2/9] ARM64 / ACPI: Prefill cpu possible/present
 maps and map logical cpu id to APIC id

On 2013年12月04日 23:47, Rob Herring wrote:
> On Tue, Dec 3, 2013 at 10:39 AM, Hanjun Guo <hanjun.guo@...aro.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@...aro.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?

I didn't see the code in the mainline, Mark Brown is
working on it now?

>>                  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.

I think possible map here is related to ACPI based CPU hot-plug,
that's why I introduce the code here, if anything I'm wrong, please
correct me.

Thanks
Hanjun
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