Re: [PATCH v1] perf symbol: Lazily compute idle and use the perf_env

[Namhyung Kim <namhyung@kernel.org>]

Hi Ian,

Sorry for the delay.

On Tue, Mar 24, 2026 at 10:14:01AM -0700, Ian Rogers wrote:
> On Mon, Mar 2, 2026 at 3:43 PM Ian Rogers <irogers@google.com> wrote:
[SNIP]
> > -       if (idle_symbols_list)
> > -               return strlist__has_entry(idle_symbols_list, name);
> > +       /*
> > +        * ppc64 uses function descriptors and appends a '.' to the
> > +        * start of every instruction address. Remove it.
> > +        */
> > +       if (name[0] == '.')

Then e_machine == EM_PPC64 can be checked here.

> > +               name++;
> > +
> > +

Two blank lines.

> > +       if (bsearch(name, idle_symbols, ARRAY_SIZE(idle_symbols),
> > +                   sizeof(idle_symbols[0]), sym_name_cmp)) {
> > +               sym->idle = SYMBOL_IDLE__IDLE;
> > +               return true;
> > +       }
> > +
> > +       if (e_machine == EM_386 || e_machine == EM_X86_64) {
> > +               if (strstarts(name, "mwait_idle") ||
> > +                   strstarts(name, "intel_idle")) {
> > +                       sym->idle = SYMBOL_IDLE__IDLE;
> > +                       return true;
> > +               }
> > +       }
> > +
> > +       if (e_machine == EM_PPC64 &&!strcmp(name, "ppc64_runlatch_off")) {
> > +               sym->idle = SYMBOL_IDLE__IDLE;
> > +               return true;
> > +       }
> >
> > -       idle_symbols_list = strlist__new(NULL, NULL);
> > +       if (e_machine == EM_S390) {
> > +               int major = 0, minor = 0;
> > +               const char *release = env && env->os_release
> > +                       ? env->os_release : perf_version_string;
> >
> > -       for (i = 0; idle_symbols[i]; i++)
> > -               strlist__add(idle_symbols_list, idle_symbols[i]);
> > +               sscanf(release, "%d.%d", &major, &minor);
> >
> > -       return strlist__has_entry(idle_symbols_list, name);
> > +               /* Before v6.10, s390 used psw_idle. */
> > +               if ((major < 6 || (major == 6 && minor < 10)) && strstarts(name, "psw_idle")) {
> > +                       sym->idle = SYMBOL_IDLE__IDLE;
> > +                       return true;
> > +               }
> > +       }
> > +
> > +       sym->idle = SYMBOL_IDLE__NOT_IDLE;
> > +       return false;
> >  }
> >
> >  static int map__process_kallsym_symbol(void *arg, const char *name,
> > @@ -785,7 +815,7 @@ static int map__process_kallsym_symbol(void *arg, const char *name,
> >          * We will pass the symbols to the filter later, in
> >          * map__split_kallsyms, when we have split the maps per module
> >          */
> > -       __symbols__insert(root, sym, !strchr(name, '['));
> > +       __symbols__insert(root, sym);
> >
> >         return 0;
> >  }
> > diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> > index 3fb5d146d9b1..508dd9f336e9 100644
> > --- a/tools/perf/util/symbol.h
> > +++ b/tools/perf/util/symbol.h
> > @@ -24,6 +24,7 @@ struct dso;
> >  struct map;
> >  struct maps;
> >  struct option;
> > +struct perf_env;
> >  struct build_id;
> >
> >  /*
> > @@ -41,6 +42,12 @@ Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
> >                              GElf_Shdr *shp, const char *name, size_t *idx);
> >  #endif
> >
> > +enum symbol_idle_kind {
> > +       SYMBOL_IDLE__UNKNOWN = 0,
> > +       SYMBOL_IDLE__NOT_IDLE = 1,
> > +       SYMBOL_IDLE__IDLE = 2,
> > +};
> > +
> >  /**
> >   * A symtab entry. When allocated this may be preceded by an annotation (see
> >   * symbol__annotation) and/or a browser_index (see symbol__browser_index).
> > @@ -56,8 +63,8 @@ struct symbol {
> >         u8              type:4;
> >         /** ELF binding type as defined for st_info. E.g. STB_WEAK or STB_GLOBAL. */
> >         u8              binding:4;
> > -       /** Set true for kernel symbols of idle routines. */
> > -       u8              idle:1;
> > +       /** Cache for symbol__is_idle. */
> > +       enum symbol_idle_kind idle:2;

I'm curious if bitfields with different types (u8 and enum) can be
placed consecutively bitwise.  There can be a lot of symbols so it
could be a concern.

Thanks,
Namhyung


> >         /** Resolvable but tools ignore it (e.g. idle routines). */
> >         u8              ignore:1;
> >         /** Symbol for an inlined function. */
> > @@ -184,8 +191,7 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss);
> >
> >  char *dso__demangle_sym(struct dso *dso, int kmodule, const char *elf_name);
> >
> > -void __symbols__insert(struct rb_root_cached *symbols, struct symbol *sym,
> > -                      bool kernel);
> > +void __symbols__insert(struct rb_root_cached *symbols, struct symbol *sym);
> >  void symbols__insert(struct rb_root_cached *symbols, struct symbol *sym);
> >  void symbols__fixup_duplicate(struct rb_root_cached *symbols);
> >  void symbols__fixup_end(struct rb_root_cached *symbols, bool is_kallsyms);
> > @@ -269,5 +275,6 @@ enum {
> >  };
> >
> >  int symbol__validate_sym_arguments(void);
> > +bool symbol__is_idle(struct symbol *sym, const struct dso *dso, const struct perf_env *env);
> >
> >  #endif /* __PERF_SYMBOL */
> > --
> > 2.53.0.473.g4a7958ca14-goog
> >