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Message-ID: <CAJOA=zMxrpukWKWLy-mNcM0OsV==yZbRLusmVuqN5H5QU-Q_mA@mail.gmail.com>
Date: Wed, 10 Aug 2011 10:25:12 -0700
From: "Turquette, Mike" <mturquette@...com>
To: Mike Turquette <mturquette@...com>, linux-kernel@...r.kernel.org,
linux-pm@...ts.linux-foundation.org, linaro-dev@...ts.linaro.org,
patches@...aro.org
Subject: Re: [PATCH 1/2] cpumask: introduce cpumask for hotpluggable CPUs
On Wed, Aug 10, 2011 at 1:42 AM, Amit Kucheria <amit.kucheria@...aro.org> wrote:
> On 11 Aug 09, Mike Turquette wrote:
>> On some platforms it is possible to have some CPUs which support CPU
>> hotplug and some which do not. Currently the prescence of an 'online'
>> sysfs entry in userspace is adequate for applications to know that a CPU
>> supports hotplug, but there is no convenient way to make the same
>> determination in the kernel.
>>
>> To better model this relationship this patch introduces a new cpumask to
>> track CPUs that support CPU hotplug operations.
>>
>> This new cpumask is populated at boot-time and remains static for the
>> life of the machine. Bits set in the mask indicate a CPU which supports
>> hotplug, but make no guarantees about whether that CPU is currently
>> online or not. Likewise a cleared bit in the mask indicates either a
>> CPU which cannot hotplug or a lack of a populated CPU.
>>
>> The purpose of this new cpumask is to aid kernel code which uses CPU to
>> take CPUs online and offline. Possible uses are as a thermal event
>> mitigation technique or as a power capping mechanism.
>>
>> Signed-off-by: Mike Turquette <mturquette@...com>
>> ---
>> include/linux/cpumask.h | 27 ++++++++++++++++++++++-----
>> kernel/cpu.c | 18 ++++++++++++++++++
>> 2 files changed, 40 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
>> index b24ac56..9eed444 100644
>> --- a/include/linux/cpumask.h
>> +++ b/include/linux/cpumask.h
>> @@ -39,10 +39,11 @@ extern int nr_cpu_ids;
>> * The following particular system cpumasks and operations manage
>> * possible, present, active and online cpus.
>> *
>> - * cpu_possible_mask- has bit 'cpu' set iff cpu is populatable
>> - * cpu_present_mask - has bit 'cpu' set iff cpu is populated
>> - * cpu_online_mask - has bit 'cpu' set iff cpu available to scheduler
>> - * cpu_active_mask - has bit 'cpu' set iff cpu available to migration
>> + * cpu_possible_mask - has bit 'cpu' set iff cpu is populatable
>> + * cpu_hotpluggable_mask - has bit 'cpu' set iff cpu is hotpluggable
>> + * cpu_present_mask - has bit 'cpu' set iff cpu is populated
>> + * cpu_online_mask - has bit 'cpu' set iff cpu available to scheduler
>> + * cpu_active_mask - has bit 'cpu' set iff cpu available to migration
>> *
>> * If !CONFIG_HOTPLUG_CPU, present == possible, and active == online.
>> *
>> @@ -51,7 +52,11 @@ extern int nr_cpu_ids;
>> * life of that system boot. The cpu_present_mask is dynamic(*),
>> * representing which CPUs are currently plugged in. And
>> * cpu_online_mask is the dynamic subset of cpu_present_mask,
>> - * indicating those CPUs available for scheduling.
>> + * indicating those CPUs available for scheduling. The
>> + * cpu_hotpluggable_mask is also fixed at boot time, as the set of CPU
>> + * id's which are possible AND can hotplug. Cleared bits in this mask
>> + * mean that either the CPU is not possible, or it is possible but does
>> + * not support CPU hotplug operations.
>> *
>> * If HOTPLUG is enabled, then cpu_possible_mask is forced to have
>> * all NR_CPUS bits set, otherwise it is just the set of CPUs that
>> @@ -61,6 +66,9 @@ extern int nr_cpu_ids;
>> * depending on what ACPI reports as currently plugged in, otherwise
>> * cpu_present_mask is just a copy of cpu_possible_mask.
>> *
>> + * If CONFIG_HOTPLUG_CPU is enabled, then cpu_hotpluggable_mask matches
>> + * the description above, otherwise it is the empty set.
>> + *
>> * (*) Well, cpu_present_mask is dynamic in the hotplug case. If not
>> * hotplug, it's a copy of cpu_possible_mask, hence fixed at boot.
>> *
>> @@ -76,6 +84,7 @@ extern int nr_cpu_ids;
>> */
>>
>> extern const struct cpumask *const cpu_possible_mask;
>> +extern const struct cpumask *const cpu_hotpluggable_mask;
>> extern const struct cpumask *const cpu_online_mask;
>> extern const struct cpumask *const cpu_present_mask;
>> extern const struct cpumask *const cpu_active_mask;
>> @@ -85,19 +94,23 @@ extern const struct cpumask *const cpu_active_mask;
>> #define num_possible_cpus() cpumask_weight(cpu_possible_mask)
>> #define num_present_cpus() cpumask_weight(cpu_present_mask)
>> #define num_active_cpus() cpumask_weight(cpu_active_mask)
>> +#define num_hotpluggable_cpus() cpumask_weight(cpu_hotpluggable_mask)
>> #define cpu_online(cpu) cpumask_test_cpu((cpu), cpu_online_mask)
>> #define cpu_possible(cpu) cpumask_test_cpu((cpu), cpu_possible_mask)
>> #define cpu_present(cpu) cpumask_test_cpu((cpu), cpu_present_mask)
>> #define cpu_active(cpu) cpumask_test_cpu((cpu), cpu_active_mask)
>> +#define cpu_hotpluggable(cpu) cpumask_test_cpu((cpu, cpu_hotpluggable_mask)
>
> missing closing bracket? ^^^^
Oops. Will fix in V2.
Thanks,
Mike
>> #else
>> #define num_online_cpus() 1U
>> #define num_possible_cpus() 1U
>> #define num_present_cpus() 1U
>> #define num_active_cpus() 1U
>> +#define num_hotpluggable_cpus() 0
>> #define cpu_online(cpu) ((cpu) == 0)
>> #define cpu_possible(cpu) ((cpu) == 0)
>> #define cpu_present(cpu) ((cpu) == 0)
>> #define cpu_active(cpu) ((cpu) == 0)
>> +#define cpu_hotpluggable(cpu) 0
>> #endif
>>
>> /* verify cpu argument to cpumask_* operators */
>> @@ -678,16 +691,20 @@ extern const DECLARE_BITMAP(cpu_all_bits, NR_CPUS);
>> #define cpu_none_mask to_cpumask(cpu_bit_bitmap[0])
>>
>> #define for_each_possible_cpu(cpu) for_each_cpu((cpu), cpu_possible_mask)
>> +#define for_each_hotpluggable_cpu(cpu) \
>> + for_each_cpu((cpu), cpu_hotpluggable_mask)
>> #define for_each_online_cpu(cpu) for_each_cpu((cpu), cpu_online_mask)
>> #define for_each_present_cpu(cpu) for_each_cpu((cpu), cpu_present_mask)
>>
>> /* Wrappers for arch boot code to manipulate normally-constant masks */
>> void set_cpu_possible(unsigned int cpu, bool possible);
>> +void set_cpu_hotpluggable(unsigned int cpu, bool hotpluggable);
>> void set_cpu_present(unsigned int cpu, bool present);
>> void set_cpu_online(unsigned int cpu, bool online);
>> void set_cpu_active(unsigned int cpu, bool active);
>> void init_cpu_present(const struct cpumask *src);
>> void init_cpu_possible(const struct cpumask *src);
>> +void init_cpu_hotpluggable(const struct cpumask *src);
>> void init_cpu_online(const struct cpumask *src);
>>
>> /**
>> diff --git a/kernel/cpu.c b/kernel/cpu.c
>> index 12b7458..8c397c9 100644
>> --- a/kernel/cpu.c
>> +++ b/kernel/cpu.c
>> @@ -536,6 +536,11 @@ static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
>> const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
>> EXPORT_SYMBOL(cpu_possible_mask);
>>
>> +static DECLARE_BITMAP(cpu_hotpluggable_bits, CONFIG_NR_CPUS) __read_mostly;
>> +const struct cpumask *const cpu_hotpluggable_mask =
>> + to_cpumask(cpu_hotpluggable_bits);
>> +EXPORT_SYMBOL(cpu_hotpluggable_mask);
>> +
>> static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
>> const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
>> EXPORT_SYMBOL(cpu_online_mask);
>> @@ -556,6 +561,14 @@ void set_cpu_possible(unsigned int cpu, bool possible)
>> cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
>> }
>>
>> +void set_cpu_hotpluggable(unsigned int cpu, bool hotpluggable)
>> +{
>> + if (hotpluggable)
>> + cpumask_set_cpu(cpu, to_cpumask(cpu_hotpluggable_bits));
>> + else
>> + cpumask_clear_cpu(cpu, to_cpumask(cpu_hotpluggable_bits));
>> +}
>> +
>> void set_cpu_present(unsigned int cpu, bool present)
>> {
>> if (present)
>> @@ -590,6 +603,11 @@ void init_cpu_possible(const struct cpumask *src)
>> cpumask_copy(to_cpumask(cpu_possible_bits), src);
>> }
>>
>> +void init_cpu_hotpluggable(const struct cpumask *src)
>> +{
>> + cpumask_copy(to_cpumask(cpu_hotpluggable_bits), src);
>> +}
>> +
>> void init_cpu_online(const struct cpumask *src)
>> {
>> cpumask_copy(to_cpumask(cpu_online_bits), src);
>> --
>> 1.7.4.1
>>
>>
>> _______________________________________________
>> linaro-dev mailing list
>> linaro-dev@...ts.linaro.org
>> http://lists.linaro.org/mailman/listinfo/linaro-dev
>
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