by James Clark

[permalink] [raw]

Subject: Re: [PATCH v2 1/7] perf: Remove duplication around EVENT_SOURCE_DEVICE_PATH

On 23/12/2022 02:39, Leo Yan wrote:
> On Thu, Dec 22, 2022 at 04:03:21PM +0000, James Clark wrote:
>> The pattern for accessing EVENT_SOURCE_DEVICE_PATH is duplicated in a
>> few places, so add two utility functions to cover it. Also just use
>> perf_pmu__scan_file() instead of pmu_type() which already does the same
>> thing.
>>
>> No functional changes.
>
> After I read the article: https://lwn.net/Articles/69419/, good to see
> this patch uses scnprintf() to replace snprintf().
>
>> Signed-off-by: James Clark <[email protected]>
>> ---
>> tools/perf/arch/arm/util/auxtrace.c | 5 +-
>> tools/perf/arch/x86/util/pmu.c | 12 +--
>> tools/perf/util/pmu.c | 110 +++++++++++-----------------
>> tools/perf/util/pmu.h | 5 +-
>> 4 files changed, 49 insertions(+), 83 deletions(-)
>>
>> diff --git a/tools/perf/arch/arm/util/auxtrace.c b/tools/perf/arch/arm/util/auxtrace.c
>> index deeb163999ce..3cb4a6a16112 100644
>> --- a/tools/perf/arch/arm/util/auxtrace.c
>> +++ b/tools/perf/arch/arm/util/auxtrace.c
>> @@ -55,17 +55,16 @@ static struct perf_pmu **find_all_arm_spe_pmus(int *nr_spes, int *err)
>>
>> static struct perf_pmu **find_all_hisi_ptt_pmus(int *nr_ptts, int *err)
>> {
>> - const char *sysfs = sysfs__mountpoint();
>> struct perf_pmu **hisi_ptt_pmus = NULL;
>> struct dirent *dent;
>> char path[PATH_MAX];
>> DIR *dir = NULL;
>> int idx = 0;
>>
>> - snprintf(path, PATH_MAX, "%s" EVENT_SOURCE_DEVICE_PATH, sysfs);
>> + perf_pmu__event_source_devices_scnprintf(path, PATH_MAX);
>
> Nitpick: since 'path' is an array, a good practice is to use
> 'sizeof(path)' rather than 'PATH_MAX' for passing the length.

Done

[...]

>>
>> @@ -983,9 +931,14 @@ static struct perf_pmu *pmu_lookup(const char *lookup_name)
>>
>> pmu->cpus = pmu_cpumask(name);
>> pmu->name = strdup(name);
>> +
>> if (!pmu->name)
>> goto err;
>>
>> + /* Read type, and ensure that 1 value (type) is successfully assigned */
>
> Maybe I don't understand well, seems to me a better comment is:
>
> /* Read type, and ensure that type value is successfully assigned (return 1) */
>

Changed it in V3. I was trying to portray that the function returns how
many variables were successfully assigned, which is slightly different
to 1 == success. But it's probably clearer your way.

>
> The rest looks good to me. With addressing above two comments:

> Reviewed-by: Leo Yan <[email protected]>

Thanks for the review.

2023-01-03 17:18:27

by James Clark

[permalink] [raw]

Subject: Re: [PATCH v2 2/7] perf: Use perf_pmu__open_file() and perf_pmu__scan_file()

On 23/12/2022 03:45, Leo Yan wrote:
> On Thu, Dec 22, 2022 at 04:03:22PM +0000, James Clark wrote:
>> Remove some code that duplicates existing methods. This requires that
>> some consts are removed because one of the existing helper methods takes
>> a struct perf_pmu instead of a name which has a non const name field.
>> But except for the tests, the strings were already non const.
>>
>> No functional changes.
>>
>> Signed-off-by: James Clark <[email protected]>
>> ---
>> tools/perf/tests/evsel-roundtrip-name.c | 3 +-
>> tools/perf/tests/parse-events.c | 3 +-
>> tools/perf/util/cputopo.c | 9 +-----
>> tools/perf/util/pmu-hybrid.c | 27 +++-------------
>> tools/perf/util/pmu-hybrid.h | 2 +-
>> tools/perf/util/pmu.c | 42 +++++++------------------
>> tools/perf/util/pmu.h | 3 +-
>> 7 files changed, 24 insertions(+), 65 deletions(-)
>>
>> diff --git a/tools/perf/tests/evsel-roundtrip-name.c b/tools/perf/tests/evsel-roundtrip-name.c
>> index e94fed901992..9bccf177f481 100644
>> --- a/tools/perf/tests/evsel-roundtrip-name.c
>> +++ b/tools/perf/tests/evsel-roundtrip-name.c
>> @@ -103,8 +103,9 @@ static int test__perf_evsel__roundtrip_name_test(struct test_suite *test __maybe
>> int subtest __maybe_unused)
>> {
>> int err = 0, ret = 0;
>> + char cpu_atom[] = "cpu_atom";
>>
>> - if (perf_pmu__has_hybrid() && perf_pmu__hybrid_mounted("cpu_atom"))
>> + if (perf_pmu__has_hybrid() && perf_pmu__hybrid_mounted(cpu_atom))
>
> After change the parameter 'name' to non const type in function
> perf_pmu__hybrid_mounted(), at here we still can pass string "cpu_atom"
> without warning, right? If so, we don't need to define a local
> variable 'cpu_atom'.
>
> [...]
>
>> -bool perf_pmu__hybrid_mounted(const char *name)
>> +bool perf_pmu__hybrid_mounted(char *name)
>> {
>> - char path[PATH_MAX];
>> - const char *sysfs;
>> - FILE *file;
>> - int n, cpu;
>> + int cpu;
>> + struct perf_pmu pmu = {.name = name};
>>
>> if (strncmp(name, "cpu_", 4))
>> return false;
>>
>> - sysfs = sysfs__mountpoint();
>> - if (!sysfs)
>> - return false;
>> -
>> - snprintf(path, PATH_MAX, CPUS_TEMPLATE_CPU, sysfs, name);
>> - if (!file_available(path))
>> - return false;
>> -
>> - file = fopen(path, "r");
>> - if (!file)
>> - return false;
>> -
>> - n = fscanf(file, "%u", &cpu);
>> - fclose(file);
>> - if (n <= 0)
>> - return false;
>> -
>> - return true;
>> + return perf_pmu__scan_file(&pmu, "cpus", "%u", &cpu) > 0;
>
> It's not necessarily to change the parameter 'name' to non const type,
> we can handle this case in two different ways.
>
> The first option is to refine the code with using the function
> perf_pmu__pathname_scnprintf() which is introduced in patch 01, thus
> we can keep using fopen() and fscanf() to read out value from 'cpus'
> entry.
>
> Another option is to define a local array 'pmu_name[PATH_MAX]' and
> then copy the input string to this array, something like:
>
> bool perf_pmu__hybrid_mounted(const char *name)
> {
> char pmu_name[PATH_MAX];
> struct perf_pmu pmu;
> int cpu;
>
> strncpy(pmu_name, name, sizeof(pmu_name));
> pmu.name = pmu_name;
>
> return perf_pmu__scan_file(&pmu, "cpus", "%u", &cpu) > 0;
> }
>
> We even can consider to dynamically allocate buffer and copy string from
> 'name' to the allocated buffer.
>

I went with the string copy way and put the consts back in V3. One minor
difference is that I had to use strlcpy() instead of strncpy() to avoid
a compiler warning about the destination buffer being the same size.

James

[...]

>> -static struct perf_cpu_map *pmu_cpumask(const char *name)
>> +static struct perf_cpu_map *pmu_cpumask(char *name)
>> {
>> - char path[PATH_MAX];
>> struct perf_cpu_map *cpus;
>> - const char *sysfs = sysfs__mountpoint();
>> const char *templates[] = {
>> - CPUS_TEMPLATE_UNCORE,
>> - CPUS_TEMPLATE_CPU,
>> + "cpumask",
>> + "cpus",
>> NULL
>> };
>> const char **template;
>> -
>> - if (!sysfs)
>> - return NULL;
>> + struct perf_pmu pmu = {.name = name};
>
> Here we also can define a local array and copy string from 'name' to
> the local array. This can allow us to provide a friendly function and
> caller doesn't need to explictly pass non const string.
>

Done