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Message-ID: <f7b3a4af-0c74-b032-bc44-b05fff1f7db5@linux.intel.com>
Date: Thu, 19 Mar 2020 09:07:21 -0400
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc: jolsa@...hat.com, peterz@...radead.org, mingo@...hat.com,
linux-kernel@...r.kernel.org, namhyung@...nel.org,
adrian.hunter@...el.com, mathieu.poirier@...aro.org,
ravi.bangoria@...ux.ibm.com, alexey.budankov@...ux.intel.com,
vitaly.slobodskoy@...el.com, pavel.gerasimov@...el.com,
mpe@...erman.id.au, eranian@...gle.com, ak@...ux.intel.com
Subject: Re: [PATCH V3 01/17] perf pmu: Add support for PMU capabilities
On 3/18/2020 3:47 PM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Mar 13, 2020 at 11:33:03AM -0700, kan.liang@...ux.intel.com escreveu:
>> From: Kan Liang <kan.liang@...ux.intel.com>
>>
>> The PMU capabilities information, which is located at
>> /sys/bus/event_source/devices/<dev>/caps, is required by perf tool.
>> For example, the max LBR information is required to stitch LBR call
>> stack.
>>
>> Add perf_pmu__caps_parse() to parse the PMU capabilities information.
>> The information is stored in a list.
>>
>> Add perf_pmu__scan_caps() to scan the capabilities one by one.
>>
>> The following patch will store the capabilities information in perf
>> header.
>>
>> Reviewed-by: Andi Kleen <ak@...ux.intel.com>
>> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
>> ---
>> tools/perf/util/pmu.c | 98 +++++++++++++++++++++++++++++++++++++++++++
>> tools/perf/util/pmu.h | 12 ++++++
>> 2 files changed, 110 insertions(+)
>>
>> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
>> index 8b99fd312aae..4cdfbb669567 100644
>> --- a/tools/perf/util/pmu.c
>> +++ b/tools/perf/util/pmu.c
>> @@ -844,6 +844,7 @@ static struct perf_pmu *pmu_lookup(const char *name)
>>
>> INIT_LIST_HEAD(&pmu->format);
>> INIT_LIST_HEAD(&pmu->aliases);
>> + INIT_LIST_HEAD(&pmu->caps);
>> list_splice(&format, &pmu->format);
>> list_splice(&aliases, &pmu->aliases);
>> list_add_tail(&pmu->list, &pmus);
>> @@ -1565,3 +1566,100 @@ int perf_pmu__scan_file(struct perf_pmu *pmu, const char *name, const char *fmt,
>> va_end(args);
>> return ret;
>> }
>> +
>> +static int perf_pmu__new_caps(struct list_head *list, char *name, char *value)
>> +{
>> + struct perf_pmu_caps *caps;
>> +
>> + caps = zalloc(sizeof(*caps));
>> + if (!caps)
>> + return -ENOMEM;
>
> Since there will be a v4 for other reasons, please combine the
> declaration plus assignment when possible, like above, i.e. make it:
>
Sure.
> + struct perf_pmu_caps *caps = zalloc(sizeof(*caps));
> +
> + if (!caps)
> + return -ENOMEM;
>
>> +
>> + caps->name = strdup(name);
>> + if (!caps->name)
>> + goto free_caps;
>> + caps->value = strndup(value, strlen(value) - 1);
>> + if (!caps->value)
>> + goto free_name;
>> + list_add_tail(&caps->list, list);
>> + return 0;
>> +
>> +free_name:
>> + free(caps->name);
>
> In these cases I think this is preferred:
>
> zfree(&caps->name);
Sure.
>
>> +free_caps:
>> + free(caps);
>> +
>> + return -ENOMEM;
>> +}
>> +
>> +/*
>> + * Reading/parsing the given pmu capabilities, which should be located at:
>> + * /sys/bus/event_source/devices/<dev>/caps as sysfs group attributes.
>> + * Return the number of capabilities
>> + */
>> +int perf_pmu__caps_parse(struct perf_pmu *pmu)
>> +{
>> + struct stat st;
>> + char caps_path[PATH_MAX];
>> + const char *sysfs = sysfs__mountpoint();
>> + DIR *caps_dir;
>> + struct dirent *evt_ent;
>> + int nr_caps = 0;
>> +
>> + if (!sysfs)
>> + return -1;
>> +
>> + snprintf(caps_path, PATH_MAX,
>> + "%s" EVENT_SOURCE_DEVICE_PATH "%s/caps", sysfs, pmu->name);
>> +
>> + if (stat(caps_path, &st) < 0)
>> + return 0; /* no error if caps does not exist */
>> +
>> + caps_dir = opendir(caps_path);
>> + if (!caps_dir)
>> + return -EINVAL;
>> +
>> + while ((evt_ent = readdir(caps_dir)) != NULL) {
>> + char path[PATH_MAX + NAME_MAX + 1];
>> + char *name = evt_ent->d_name;
>> + char value[128];
>> + FILE *file;
>> +
>> + if (!strcmp(name, ".") || !strcmp(name, ".."))
>> + continue;
>> +
>> + snprintf(path, sizeof(path), "%s/%s", caps_path, name);
>> +
>> + file = fopen(path, "r");
>> + if (!file)
>> + break;
>
> I haven't looked at what is in such directories that would justify still
> returning whatever was read so far when failing to read one of its
> files, is this sensible? Care to explain a bit why you think so? Looks
> fishy :-\
There is no dependency among the 'capabilities'. If perf fails to read
one, it should not impact others.
Yes, 'continue' looks better here.
>
>> +
>> + if (!fgets(value, sizeof(value), file) ||
>> + (perf_pmu__new_caps(&pmu->caps, name, value) < 0)) {
>> + fclose(file);
>> + break;
>> + }
>> +
>> + nr_caps++;
>> + fclose(file);
>> + }
>> +
>> + closedir(caps_dir);
>> +
>> + return nr_caps;
>> +}
>> +
>> +struct perf_pmu_caps *perf_pmu__scan_caps(struct perf_pmu *pmu,
>> + struct perf_pmu_caps *caps)
>> +{
>> + if (!pmu)
>> + return NULL;
>> +
>> + if (!caps)
>> + caps = list_prepare_entry(caps, &pmu->caps, list);
>> +
>> + list_for_each_entry_continue(caps, &pmu->caps, list)
>> + return caps;
>
> Why not:
>
> return caps ? list_next_entry(caps) : list_first_entry(&pmu->caps, struct perf_pmu_caps, list);
>
> Nah, it'll return the head after the last entry, not NULL, argh.
>
> Anyway, looks like a confusing API :-\
>
> I'll see how it is used in the following patches...
As suggested in other thread, I will use list_for_each_entry() to
replace in v4.
Thanks,
Kan
>
>> +
>> + return NULL;
>> +}
>> diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
>> index 6737e3d5d568..a228e27ae462 100644
>> --- a/tools/perf/util/pmu.h
>> +++ b/tools/perf/util/pmu.h
>> @@ -21,6 +21,12 @@ enum {
>>
>> struct perf_event_attr;
>>
>> +struct perf_pmu_caps {
>> + char *name;
>> + char *value;
>> + struct list_head list;
>> +};
>> +
>> struct perf_pmu {
>> char *name;
>> __u32 type;
>> @@ -32,6 +38,7 @@ struct perf_pmu {
>> struct perf_cpu_map *cpus;
>> struct list_head format; /* HEAD struct perf_pmu_format -> list */
>> struct list_head aliases; /* HEAD struct perf_pmu_alias -> list */
>> + struct list_head caps; /* HEAD struct perf_pmu_caps -> list */
>> struct list_head list; /* ELEM */
>> };
>>
>> @@ -102,4 +109,9 @@ struct pmu_events_map *perf_pmu__find_map(struct perf_pmu *pmu);
>>
>> int perf_pmu__convert_scale(const char *scale, char **end, double *sval);
>>
>> +int perf_pmu__caps_parse(struct perf_pmu *pmu);
>> +
>> +struct perf_pmu_caps *perf_pmu__scan_caps(struct perf_pmu *pmu,
>> + struct perf_pmu_caps *caps);
>> +
>> #endif /* __PMU_H */
>> --
>> 2.17.1
>>
>
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