Re: [PATCH v3 1/2] ACPI/PPTT: Add support for ACPI 6.3 thread flag

[John Garry <john.garry@huawei.com>]

在 03/07/2019 17:24, Rafael J. Wysocki 写道:
> On Fri, Jun 28, 2019 at 8:15 PM Jeremy Linton <jeremy.linton@arm.com> wrote:
>>
>> ACPI 6.3 adds a flag to the CPU node to indicate whether
>> the given PE is a thread. Add a function to return that
>> information for a given linux logical CPU.
>>
>> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
>> ---
>>   drivers/acpi/pptt.c  | 62 +++++++++++++++++++++++++++++++++++++++++++-
>>   include/linux/acpi.h |  5 ++++
>>   2 files changed, 66 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
>> index b72e6afaa8fb..bb6196422fad 100644
>> --- a/drivers/acpi/pptt.c
>> +++ b/drivers/acpi/pptt.c
>> @@ -517,6 +517,52 @@ static int find_acpi_cpu_topology_tag(unsigned int cpu, int level, int flag)
>>          return retval;
>>   }
>>
>> +/**
>> + * check_acpi_cpu_flag() - Determine if CPU node has a flag set
>> + * @cpu: Kernel logical CPU number
>> + * @rev: The PPTT revision defining the flag
>> + * @flag: The flag itself
>> + *
>> + * Check the node representing a CPU for a given flag.
>> + *
>> + * Return: -ENOENT if the PPTT doesn't exist, the CPU cannot be found or
>> + *        the table revision isn't new enough.
>> + *        1, any passed flag set
>> + *        0, flag unset
>> + */
>> +static int check_acpi_cpu_flag(unsigned int cpu, int rev, u32 flag)
> 
> Why not bool?
> 
>> +{
>> +       struct acpi_table_header *table;
>> +       acpi_status status;
>> +       u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);
>> +       struct acpi_pptt_processor *cpu_node = NULL;
>> +       int ret = -ENOENT;
>> +       static int saved_pptt_rev = -1;
>> +
>> +       /* Cache the PPTT revision to avoid repeat table get/put on failure */
> 
> This is a rather questionable optimization.
> 
> Does the extra table get/put really matter?

I would have made saved_pptt_rev a global, but, indeed, caching the 
value is not so important.

> 
>> +       if (saved_pptt_rev > -1 && saved_pptt_rev < rev)
>> +               return -ENOENT;
> 
> It should be fine to return 'false' here, shouldn't it?
> 
>> +
>> +       status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
>> +       if (ACPI_FAILURE(status)) {
>> +               saved_pptt_rev = 0;
>> +               acpi_pptt_warn_missing();
>> +               return ret;
> 
> And here?
> 
>> +       }
>> +
>> +       saved_pptt_rev = table->revision;
>> +
>> +       if (saved_pptt_rev >= rev)
>> +               cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
>> +
>> +       if (cpu_node)
>> +               ret = (cpu_node->flags & flag) != 0;
> 
> And this can be
> 
> ret = !!(cpu_node->flags & flag);
> 
>> +
>> +       acpi_put_table(table);
>> +
>> +       return ret;
>> +}
>> +
>>   /**
>>    * acpi_find_last_cache_level() - Determines the number of cache levels for a PE
>>    * @cpu: Kernel logical CPU number
>> @@ -581,6 +627,21 @@ int cache_setup_acpi(unsigned int cpu)
>>          return status;
>>   }
>>
>> +/**
>> + * acpi_pptt_cpu_is_thread() - Determine if CPU is a thread
>> + * @cpu: Kernel logical CPU number
>> + *
>> + *
>> + * Return: 1, a thread
>> + *         0, not a thread
>> + *         -ENOENT ,if the PPTT doesn't exist, the CPU cannot be found or
>> + *         the table revision isn't new enough.
>> + */
>> +int acpi_pptt_cpu_is_thread(unsigned int cpu)
>> +{
>> +       return check_acpi_cpu_flag(cpu, 2, ACPI_PPTT_ACPI_PROCESSOR_IS_THREAD);
>> +}

You could also consider the following to avoid the tri-state return value:

bool acpi_pptt_cpu_find_threaded(unsigned int cpu, bool *is_threaded)

>> +
>>   /**
>>    * find_acpi_cpu_topology() - Determine a unique topology value for a given CPU
>>    * @cpu: Kernel logical CPU number
>> @@ -641,7 +702,6 @@ int find_acpi_cpu_cache_topology(unsigned int cpu, int level)
>>          return ret;
>>   }
>>
>> -
>>   /**
>>    * find_acpi_cpu_topology_package() - Determine a unique CPU package value
>>    * @cpu: Kernel logical CPU number
>> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
>> index d315d86844e4..3e339375e213 100644
>> --- a/include/linux/acpi.h
>> +++ b/include/linux/acpi.h
>> @@ -1301,10 +1301,15 @@ static inline int lpit_read_residency_count_address(u64 *address)
>>   #endif
>>
>>   #ifdef CONFIG_ACPI_PPTT
>> +int acpi_pptt_cpu_is_thread(unsigned int cpu);
>>   int find_acpi_cpu_topology(unsigned int cpu, int level);
>>   int find_acpi_cpu_topology_package(unsigned int cpu);
>>   int find_acpi_cpu_cache_topology(unsigned int cpu, int level);
>>   #else
>> +static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
>> +{
>> +       return -EINVAL;
>> +}
>>   static inline int find_acpi_cpu_topology(unsigned int cpu, int level)
>>   {
>>          return -EINVAL;
>> --
>> 2.21.0
>>
> 
> .
>