Re: [PATCH v5 2/4] perf tools arm64: Add support for get_cpuid_str function.

[Ganapatrao Kulkarni]

On Wed, Aug 23, 2017 at 3:47 PM, Will Deacon <will.deacon@xxxxxxx> wrote:
> On Wed, Aug 16, 2017 at 12:40:46PM +0530, Ganapatrao Kulkarni wrote:
>> function get_cpuid_str returns MIDR string of the first online
>> cpu from the range of cpus associated with the pmu core device.
>>
>> Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@xxxxxxxxxx>
>> ---
>>  tools/perf/arch/arm64/util/Build    |  1 +
>>  tools/perf/arch/arm64/util/header.c | 61 +++++++++++++++++++++++++++++++++++++
>>  2 files changed, 62 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..713ef17
>> --- /dev/null
>> +++ b/tools/perf/arch/arm64/util/header.c
>> @@ -0,0 +1,61 @@
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <api/fs/fs.h>
>> +#include "header.h"
>> +
>> +#define MIDR "/regs/identification/midr_el1"
>> +#define MIDR_SIZE 128
>
> Why is this so big?

ok, i will reduce it to exact size(19)
>
>> +char *get_cpuid_str(struct perf_pmu *pmu)
>> +{
>> +     char *buf = NULL;
>> +     char *temp = NULL;
>> +     char path[PATH_MAX];
>> +     const char *sysfs = sysfs__mountpoint();
>> +     int cpu;
>> +     unsigned long long midr = 0;
>> +     struct cpu_map *cpus;
>> +     FILE *file;
>> +
>> +     if (!sysfs || !pmu->cpus)
>> +             return NULL;
>> +
>> +     buf = malloc(MIDR_SIZE);
>> +     if (!buf)
>> +             return NULL;
>> +
>> +     /* read midr from list of cpus mapped to this pmu */
>> +     cpus = cpu_map__get(pmu->cpus);
>> +     for (cpu = 0; cpu < cpus->nr; cpu++) {
>> +             scnprintf(path, PATH_MAX, "%s/devices/system/cpu/cpu%d"MIDR,
>> +                             sysfs, cpus->map[cpu]);
>> +
>> +             file = fopen(path, "r");
>> +             if (!file) {
>> +                     pr_err("fopen failed for file %s\n", path);
>
> pr_debug instead? It's not fatal if a CPU is hotplugged off and you can't
> read its midr.

ok
>
>> +                     continue;
>> +             }
>> +
>> +             temp = fgets(buf, MIDR_SIZE, file);
>> +             if (!temp)
>> +                     continue;
>
> Do you actually need a temporary variable for this?

ok
>
>> +             fclose(file);
>> +
>> +             /* Ignore/clear Variant[23:20] and
>> +              * Revision[3:0] of MIDR
>> +              */
>> +             midr = strtoll(buf, NULL, 16);
>> +             midr &= (~(0xf << 20 | 0xf));
>
> If midr really needs to be unsigned long long (u64 might be better), then
> you need to fix these immediates to have a ULL suffix.

yes, will use u64
>
> Can you use the GENMASK_ULL macro to generate the MIDR mask, or is that
> not available here?

it is not defined in tools/include/linux/bitops.h
>
>> +             scnprintf(buf, MIDR_SIZE, "0x%016llx", midr);
>> +             /* got midr break loop */
>> +             break;
>> +     }
>> +
>> +     if (!midr) {
>> +             free(buf);
>> +             buf = NULL;
>
> If you want the pr_err, here would seem more appropriate because at this
> point we've actually failed.

thanks, makes sense.
>
> Will
>
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thanks
Ganapat