linux-kernel - Re: [PATCH 2/3] perf tools arm64: implement function get_cpuid

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Message-ID: <CAFpQJXU3Gn4H2tZT3BEfEh=Q=NS_4fOgOu=21nPZUcdk6qf87w@mail.gmail.com>
Date:   Wed, 5 Apr 2017 14:48:57 +0530
From:   Ganapatrao Kulkarni <gpkulkarni@...il.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Will Deacon <Will.Deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, peterz@...radead.org,
        Ingo Molnar <mingo@...hat.com>, jnair@...iumnetworks.com
Subject: Re: [PATCH 2/3] perf tools arm64: implement function get_cpuid_str

On Tue, Apr 4, 2017 at 5:55 PM, Mark Rutland <mark.rutland@....com> wrote:
> On Tue, Apr 04, 2017 at 01:06:42PM +0530, Ganapatrao Kulkarni wrote:
>> function get_cpuid_str returns midr_el1 value from first
>> online cpu available.
>
> This isn't globally the same (e.g. in big.LITTLE systems).
>
> It would be far better to have the function take a PMU, and look at the
> first CPU in that PMU's mask.

thanks, will do.
>
> Thanks,
> Mark.
>
>>
>> Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>
>> ---
>>  tools/perf/arch/arm64/util/Build    |  1 +
>>  tools/perf/arch/arm64/util/header.c | 51 +++++++++++++++++++++++++++++++++++++
>>  2 files changed, 52 insertions(+)
>>  create mode 100644 tools/perf/arch/arm64/util/header.c
>>
>> diff --git a/tools/perf/arch/arm64/util/Build b/tools/perf/arch/arm64/util/Build
>> index cef6fb3..b1ab72d 100644
>> --- a/tools/perf/arch/arm64/util/Build
>> +++ b/tools/perf/arch/arm64/util/Build
>> @@ -1,3 +1,4 @@
>> +libperf-y += header.o
>>  libperf-$(CONFIG_DWARF)     += dwarf-regs.o
>>  libperf-$(CONFIG_LOCAL_LIBUNWIND) += unwind-libunwind.o
>>
>> diff --git a/tools/perf/arch/arm64/util/header.c b/tools/perf/arch/arm64/util/header.c
>> new file mode 100644
>> index 0000000..c0468fe
>> --- /dev/null
>> +++ b/tools/perf/arch/arm64/util/header.c
>> @@ -0,0 +1,51 @@
>> +#include <fnmatch.h>
>> +#include <dirent.h>
>> +#include <unistd.h>
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <string.h>
>> +#include <linux/stringify.h>
>> +#include "header.h"
>> +#include "util.h"
>> +
>> +#define LINUX_SYS_CPU_DIRECTORY "/sys/devices/system/cpu/"
>> +#define MIDR "/regs/identification/midr_el1"
>> +
>> +char *get_cpuid_str(void)
>> +{
>> +     char *buf = malloc(128);
>> +     FILE *file;
>> +     char *ret = NULL;
>> +     int cpu , nr_cpu;
>> +     char sys_file[256];
>> +
>> +     sprintf(sys_file, LINUX_SYS_CPU_DIRECTORY"kernel_max");
>> +
>> +     file = fopen(sys_file, "r");
>> +     if (!file)
>> +             return ret;
>> +
>> +     if (fscanf(file, "%d", &nr_cpu) != 1)
>> +             return ret;
>> +
>> +     /* kernel_max returns nr_cpu -1 */
>> +     nr_cpu++;
>> +
>> +     /*iterate till you read midr of first online cpu */
>> +     for(cpu = 0; cpu < nr_cpu; cpu++)
>> +     {
>> +             sprintf(sys_file, LINUX_SYS_CPU_DIRECTORY"cpu%d"MIDR, cpu);
>> +             file = fopen(sys_file, "r");
>> +             if (file) {
>> +                     ret = fgets(buf, 128, file);
>> +                     if (ret) {
>> +                             buf[strlen(buf)-1] ='\0';
>> +                             fclose(file);
>> +                             return buf;
>> +                     }
>> +                     fclose(file);
>> +             }
>> +     }
>> +     free(buf);
>> +     return ret;
>> +}
>> --
>> 1.8.1.4
>>

thanks
Ganapat