Re: [PATCH v1] perf pmus: Make PMU alias name loading lazy

[Namhyung Kim]

Hi Ian,

On Sun, Sep 24, 2023 at 11:24 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> PMU alias names were computed when the first perf_pmu is created,
> scanning all PMUs in event sources for a file called alias that
> generally doesn't exist. Switch to trying to load the file when all
> PMU related files are loaded in lookup. This would cause a PMU name
> lookup of an alias name to fail if no PMUs were loaded, so in that
> case all PMUs are loaded and the find repeated. The overhead is
> similar but in the (very) general case not all PMUs are scanned for
> the alias file.
>
> As the overhead occurs once per invocation it doesn't show in perf
> bench internals pmu-scan. On a tigerlake machine, the number of openat
> system calls for an event of cpu/cycles/ with perf stat reduces from
> 94 to 69 (ie 25 fewer openat calls).

I think the pmu-scan bench could show the difference as it
calls perf_pmu__destroy() in the loop body.  So every call to
perf_pmu__scan() should start from nothing, right?

>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>

Maybe we can load event aliases and formats lazily later.
Anyway, it looks good to me.

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung


> ---
>  tools/perf/arch/x86/util/pmu.c | 139 ---------------------------------
>  tools/perf/util/pmu.c          |  39 ++++-----
>  tools/perf/util/pmu.h          |   2 -
>  tools/perf/util/pmus.c         |  10 +++
>  4 files changed, 31 insertions(+), 159 deletions(-)
>
> diff --git a/tools/perf/arch/x86/util/pmu.c b/tools/perf/arch/x86/util/pmu.c
> index f428cffb0378..8b53ca468a50 100644
> --- a/tools/perf/arch/x86/util/pmu.c
> +++ b/tools/perf/arch/x86/util/pmu.c
> @@ -17,15 +17,6 @@
>  #include "../../../util/pmus.h"
>  #include "env.h"
>
> -struct pmu_alias {
> -       char *name;
> -       char *alias;
> -       struct list_head list;
> -};
> -
> -static LIST_HEAD(pmu_alias_name_list);
> -static bool cached_list;
> -
>  struct perf_event_attr *perf_pmu__get_default_config(struct perf_pmu *pmu __maybe_unused)
>  {
>  #ifdef HAVE_AUXTRACE_SUPPORT
> @@ -41,136 +32,6 @@ struct perf_event_attr *perf_pmu__get_default_config(struct perf_pmu *pmu __mayb
>         return NULL;
>  }
>
> -static void pmu_alias__delete(struct pmu_alias *pmu_alias)
> -{
> -       if (!pmu_alias)
> -               return;
> -
> -       zfree(&pmu_alias->name);
> -       zfree(&pmu_alias->alias);
> -       free(pmu_alias);
> -}
> -
> -static struct pmu_alias *pmu_alias__new(char *name, char *alias)
> -{
> -       struct pmu_alias *pmu_alias = zalloc(sizeof(*pmu_alias));
> -
> -       if (pmu_alias) {
> -               pmu_alias->name = strdup(name);
> -               if (!pmu_alias->name)
> -                       goto out_delete;
> -
> -               pmu_alias->alias = strdup(alias);
> -               if (!pmu_alias->alias)
> -                       goto out_delete;
> -       }
> -       return pmu_alias;
> -
> -out_delete:
> -       pmu_alias__delete(pmu_alias);
> -       return NULL;
> -}
> -
> -static int setup_pmu_alias_list(void)
> -{
> -       int fd, dirfd;
> -       DIR *dir;
> -       struct dirent *dent;
> -       struct pmu_alias *pmu_alias;
> -       char buf[MAX_PMU_NAME_LEN];
> -       FILE *file;
> -       int ret = -ENOMEM;
> -
> -       dirfd = perf_pmu__event_source_devices_fd();
> -       if (dirfd < 0)
> -               return -1;
> -
> -       dir = fdopendir(dirfd);
> -       if (!dir)
> -               return -errno;
> -
> -       while ((dent = readdir(dir))) {
> -               if (!strcmp(dent->d_name, ".") ||
> -                   !strcmp(dent->d_name, ".."))
> -                       continue;
> -
> -               fd = perf_pmu__pathname_fd(dirfd, dent->d_name, "alias", O_RDONLY);
> -               if (fd < 0)
> -                       continue;
> -
> -               file = fdopen(fd, "r");
> -               if (!file)
> -                       continue;
> -
> -               if (!fgets(buf, sizeof(buf), file)) {
> -                       fclose(file);
> -                       continue;
> -               }
> -
> -               fclose(file);
> -
> -               /* Remove the last '\n' */
> -               buf[strlen(buf) - 1] = 0;
> -
> -               pmu_alias = pmu_alias__new(dent->d_name, buf);
> -               if (!pmu_alias)
> -                       goto close_dir;
> -
> -               list_add_tail(&pmu_alias->list, &pmu_alias_name_list);
> -       }
> -
> -       ret = 0;
> -
> -close_dir:
> -       closedir(dir);
> -       return ret;
> -}
> -
> -static const char *__pmu_find_real_name(const char *name)
> -{
> -       struct pmu_alias *pmu_alias;
> -
> -       list_for_each_entry(pmu_alias, &pmu_alias_name_list, list) {
> -               if (!strcmp(name, pmu_alias->alias))
> -                       return pmu_alias->name;
> -       }
> -
> -       return name;
> -}
> -
> -const char *pmu_find_real_name(const char *name)
> -{
> -       if (cached_list)
> -               return __pmu_find_real_name(name);
> -
> -       setup_pmu_alias_list();
> -       cached_list = true;
> -
> -       return __pmu_find_real_name(name);
> -}
> -
> -static const char *__pmu_find_alias_name(const char *name)
> -{
> -       struct pmu_alias *pmu_alias;
> -
> -       list_for_each_entry(pmu_alias, &pmu_alias_name_list, list) {
> -               if (!strcmp(name, pmu_alias->name))
> -                       return pmu_alias->alias;
> -       }
> -       return NULL;
> -}
> -
> -const char *pmu_find_alias_name(const char *name)
> -{
> -       if (cached_list)
> -               return __pmu_find_alias_name(name);
> -
> -       setup_pmu_alias_list();
> -       cached_list = true;
> -
> -       return __pmu_find_alias_name(name);
> -}
> -
>  int perf_pmus__num_mem_pmus(void)
>  {
>         /* AMD uses IBS OP pmu and not a core PMU for perf mem/c2c */
> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> index 0d81c059c91c..0f5c6ed257a8 100644
> --- a/tools/perf/util/pmu.c
> +++ b/tools/perf/util/pmu.c
> @@ -937,16 +937,27 @@ perf_pmu__get_default_config(struct perf_pmu *pmu __maybe_unused)
>         return NULL;
>  }
>
> -const char * __weak
> -pmu_find_real_name(const char *name)
> +static char *pmu_find_alias_name(struct perf_pmu *pmu, int dirfd)
>  {
> -       return name;
> -}
> +       FILE *file = perf_pmu__open_file_at(pmu, dirfd, "alias");
> +       char *line = NULL;
> +       size_t line_len = 0;
> +       ssize_t ret;
>
> -const char * __weak
> -pmu_find_alias_name(const char *name __maybe_unused)
> -{
> -       return NULL;
> +       if (!file)
> +               return NULL;
> +
> +       ret = getline(&line, &line_len, file);
> +       if (ret < 0) {
> +               fclose(file);
> +               return NULL;
> +       }
> +       /* Remove trailing newline. */
> +       if (ret > 0 && line[ret - 1] == '\n')
> +               line[--ret] = '\0';
> +
> +       fclose(file);
> +       return line;
>  }
>
>  static int pmu_max_precise(int dirfd, struct perf_pmu *pmu)
> @@ -957,12 +968,10 @@ static int pmu_max_precise(int dirfd, struct perf_pmu *pmu)
>         return max_precise;
>  }
>
> -struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char *lookup_name)
> +struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char *name)
>  {
>         struct perf_pmu *pmu;
>         __u32 type;
> -       const char *name = pmu_find_real_name(lookup_name);
> -       const char *alias_name;
>
>         pmu = zalloc(sizeof(*pmu));
>         if (!pmu)
> @@ -995,18 +1004,12 @@ struct perf_pmu *perf_pmu__lookup(struct list_head *pmus, int dirfd, const char
>         pmu->is_core = is_pmu_core(name);
>         pmu->cpus = pmu_cpumask(dirfd, name, pmu->is_core);
>
> -       alias_name = pmu_find_alias_name(name);
> -       if (alias_name) {
> -               pmu->alias_name = strdup(alias_name);
> -               if (!pmu->alias_name)
> -                       goto err;
> -       }
> -
>         pmu->type = type;
>         pmu->is_uncore = pmu_is_uncore(dirfd, name);
>         if (pmu->is_uncore)
>                 pmu->id = pmu_id(name);
>         pmu->max_precise = pmu_max_precise(dirfd, pmu);
> +       pmu->alias_name = pmu_find_alias_name(pmu, dirfd);
>         pmu->events_table = perf_pmu__find_events_table(pmu);
>         pmu_add_sys_aliases(pmu);
>         list_add_tail(&pmu->list, pmus);
> diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
> index 04b317b17d66..bc807729a7cd 100644
> --- a/tools/perf/util/pmu.h
> +++ b/tools/perf/util/pmu.h
> @@ -251,8 +251,6 @@ void perf_pmu__warn_invalid_formats(struct perf_pmu *pmu);
>
>  int perf_pmu__match(const char *pattern, const char *name, const char *tok);
>
> -const char *pmu_find_real_name(const char *name);
> -const char *pmu_find_alias_name(const char *name);
>  double perf_pmu__cpu_slots_per_cycle(void);
>  int perf_pmu__event_source_devices_scnprintf(char *pathname, size_t size);
>  int perf_pmu__pathname_scnprintf(char *buf, size_t size,
> diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
> index 64e798e68a2d..ce4931461741 100644
> --- a/tools/perf/util/pmus.c
> +++ b/tools/perf/util/pmus.c
> @@ -37,6 +37,8 @@ static LIST_HEAD(other_pmus);
>  static bool read_sysfs_core_pmus;
>  static bool read_sysfs_all_pmus;
>
> +static void pmu_read_sysfs(bool core_only);
> +
>  int pmu_name_len_no_suffix(const char *str, unsigned long *num)
>  {
>         int orig_len, len;
> @@ -124,6 +126,14 @@ struct perf_pmu *perf_pmus__find(const char *name)
>         pmu = perf_pmu__lookup(core_pmu ? &core_pmus : &other_pmus, dirfd, name);
>         close(dirfd);
>
> +       if (!pmu) {
> +               /*
> +                * Looking up an inidividual PMU failed. This may mean name is
> +                * an alias, so read the PMUs from sysfs and try to find again.
> +                */
> +               pmu_read_sysfs(core_pmu);
> +               pmu = pmu_find(name);
> +       }
>         return pmu;
>  }
>
> --
> 2.42.0.515.g380fc7ccd1-goog
>