Re: [Powerpc-utils-devel] [PATCH] Fix ppc64_cpu --threads-per-core when --smt value set

[Nathan F. <nf...@li...>]

On 01/07/2015 01:01 AM, Vasant Hegde wrote:
> On 12/23/2014 12:08 PM, Mamatha Inamdar wrote:
>> Problem: ppc64_cpu --threads-per-core gives wrong data when --smt value set
>>
>> This patch will resolve the above issue and display the correct values of threads-per-core
>> for the ppc64_cpu command when --smt value is set.
>>
>> I have used the following equation to calculate threads_per_core as per lscpu command.
>>
>> 	threads_per_core = nthreads / ncores

I think there may be a slight misunderstanding between the threads-per-core
option for the ppc64_cou command and what lscpu reports.

The threads-per-core option to the ppc64_cpu command reports the number of
threads that a core contains, not the number of online threads per core.

If you want to know the number of online threads per core you need to use the
--info or --smt option.

-Nathan

>>
>> ***********************************************
>> Test results:
>>
>> CASE 1:
>>
>> ./src/ppc64_cpu --smt=on
>> [root@llmjuno03b powerpc-utils]# ./src/ppc64_cpu --threads-per-core
>> Threads per core: 4
>>
>> lscpu output:
>> Thread(s) per core:    4
>> ------------------------------------------
>> CASE 2:
>>
>> ./src/ppc64_cpu --smt=2
>> [root@llmjuno03b powerpc-utils]# ./src/ppc64_cpu --threads-per-core
>> Threads per core: 2
>>
>> lscpu output:
>> Thread(s) per core:    2
>> --------------------------------------------------
>> CASE 3:
>>
>> ./src/ppc64_cpu --smt=1
>> [root@llmjuno03b powerpc-utils]# ./src/ppc64_cpu --threads-per-core
>> Threads per core: 1
>>
>> lscpu output:
>> Thread(s) per core:    1
>> -------------------------------------------------
>>
>> Signed-off-by: Mamatha Inamdar <mam...@li...>
>> ---
>>   src/ppc64_cpu.c |   15 ++++++++++++++-
>>   1 file changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/ppc64_cpu.c b/src/ppc64_cpu.c
>> index 4df4cdc..a3cfed0 100644
>> --- a/src/ppc64_cpu.c
>> +++ b/src/ppc64_cpu.c
>> @@ -56,6 +56,7 @@ static int counters[MAX_NR_CPUS];
>>   static int threads_per_cpu = 0;
>>   static int cpus_in_system = 0;
>>   static int threads_in_system = 0;
>> +static int threads_per_core = 0;
> 
> Why do you need another global variable ? can't you just print " nthreads / 
> cpus_in_system" ?
> 
>>
>>   static int do_info(void);
>>
>> @@ -529,9 +530,21 @@ static int do_smt(char *state)
>>   	return rc;
>>   }
>>
>> +/* Threads per core */
>>   static inline void do_threads_per_core()
>>   {
>> -	printf("Threads per core: %d\n", threads_per_cpu);
>> +	int i, j;
>> +	int nthreads;    /* number of threads online */
> 
> initialize nthreads ?
> 
> 
>> +
>> +	/* Calculate number of threads present on the system */
>> +	for (j = 0; j < threads_in_system; j += threads_per_cpu) {
>> +		for (i = 0; i < threads_per_cpu; i++)
>> +			nthreads += cpu_online(j + i);
>> +	}
> 
> Can we have different cores with different SMT level?
> 
> -Vasant
> 
>> +
>> +	/* Calculate threads per core = nthreads / ncores */
>> +	threads_per_core = nthreads / cpus_in_system;
>> +	printf("Threads per core: %d\n", threads_per_core);
>>   }
>>
>>   static int do_subcores_per_core(char *state)
>>
>>
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> 
> 
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