Re: [PATCH v2] perf symbol: Lazily compute idle and use the perf_env

Ian Rogers
2026-03-26T15:11:58Z

On Thu, Mar 26, 2026 at 12:20 AM Honglei Wang <jameshongleiwang@126.com> wrote:
>
> Hi Ian,
>
> On 3/26/26 12:18 AM, Ian Rogers wrote:
> > Move the idle boolean to a helper symbol__is_idle function. In the
> > function lazily compute whether a symbol is an idle function taking
> > into consideration the kernel version and architecture of the
> > machine. As symbols__insert no longer needs to know if a symbol is for
> > the kernel, remove the argument.
> >
> > This change is inspired by mailing list discussion, particularly from
> > Thomas Richter <tmricht@linux.ibm.com> and Heiko Carstens
> > <hca@linux.ibm.com>:
> > https://lore.kernel.org/lkml/20260219113850.354271-1-tmricht@linux.ibm.com/
> >
> > The change switches x86 matches to use strstarts which means
> > intel_idle_irq is matched as part of strstarts(name, "intel_idle"), a
> > change suggested by Honglei Wang <jameshongleiwang@126.com> in:
> > https://lore.kernel.org/lkml/20260323085255.98173-1-jameshongleiwang@126.com/
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> > v1: https://lore.kernel.org/lkml/20260302234343.564937-1-irogers@google.com/
> > ---
> > tools/perf/builtin-top.c | 6 +-
> > tools/perf/util/symbol-elf.c | 2 +-
> > tools/perf/util/symbol.c | 105 ++++++++++++++++++++++-------------
> > tools/perf/util/symbol.h | 15 +++--
> > 4 files changed, 84 insertions(+), 44 deletions(-)
> >
> > diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> > index 37950efb28ac..bdc1c761cd61 100644
> > --- a/tools/perf/builtin-top.c
> > +++ b/tools/perf/builtin-top.c
> > @@ -751,6 +751,7 @@ static void perf_event__process_sample(const struct perf_tool *tool,
> > {
> > struct perf_top *top = container_of(tool, struct perf_top, tool);
> > struct addr_location al;
> > + struct dso *dso = NULL;
> >
> > if (!machine && perf_guest) {
> > static struct intlist *seen;
> > @@ -830,7 +831,10 @@ static void perf_event__process_sample(const struct perf_tool *tool,
> > }
> > }
> >
> > - if (al.sym == NULL || !al.sym->idle) {
> > + if (al.map)
> > + dso = map__dso(al.map);
> > +
> > + if (al.sym == NULL || !symbol__is_idle(al.sym, dso, machine->env)) {
> > struct hists *hists = evsel__hists(evsel);
> > struct hist_entry_iter iter = {
> > .evsel = evsel,
> > diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> > index 3cd4e5a03cc5..9fabf5146d89 100644
> > --- a/tools/perf/util/symbol-elf.c
> > +++ b/tools/perf/util/symbol-elf.c
> > @@ -1723,7 +1723,7 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
> >
> > arch__sym_update(f, &sym);
> >
> > - __symbols__insert(dso__symbols(curr_dso), f, dso__kernel(dso));
> > + __symbols__insert(dso__symbols(curr_dso), f);
> > nr++;
> > }
> > dso__put(curr_dso);
> > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> > index ce9195717f44..1a357af93a0a 100644
> > --- a/tools/perf/util/symbol.c
> > +++ b/tools/perf/util/symbol.c
> > @@ -25,6 +25,8 @@
> > #include "demangle-ocaml.h"
> > #include "demangle-rust-v0.h"
> > #include "dso.h"
> > +#include "dwarf-regs.h"
> > +#include "env.h"
> > #include "util.h" // lsdir()
> > #include "event.h"
> > #include "machine.h"
> > @@ -50,7 +52,6 @@
> >
> > static int dso__load_kernel_sym(struct dso *dso, struct map *map);
> > static int dso__load_guest_kernel_sym(struct dso *dso, struct map *map);
> > -static bool symbol__is_idle(const char *name);
> >
> > int vmlinux_path__nr_entries;
> > char **vmlinux_path;
> > @@ -357,8 +358,7 @@ void symbols__delete(struct rb_root_cached *symbols)
> > }
> > }
> >
> > -void __symbols__insert(struct rb_root_cached *symbols,
> > - struct symbol *sym, bool kernel)
> > +void __symbols__insert(struct rb_root_cached *symbols, struct symbol *sym)
> > {
> > struct rb_node **p = &symbols->rb_root.rb_node;
> > struct rb_node *parent = NULL;
> > @@ -366,17 +366,6 @@ void __symbols__insert(struct rb_root_cached *symbols,
> > struct symbol *s;
> > bool leftmost = true;
> >
> > - if (kernel) {
> > - const char *name = sym->name;
> > - /*
> > - * ppc64 uses function descriptors and appends a '.' to the
> > - * start of every instruction address. Remove it.
> > - */
> > - if (name[0] == '.')
> > - name++;
> > - sym->idle = symbol__is_idle(name);
> > - }
> > -
> > while (*p != NULL) {
> > parent = *p;
> > s = rb_entry(parent, struct symbol, rb_node);
> > @@ -393,7 +382,7 @@ void __symbols__insert(struct rb_root_cached *symbols,
> >
> > void symbols__insert(struct rb_root_cached *symbols, struct symbol *sym)
> > {
> > - __symbols__insert(symbols, sym, false);
> > + __symbols__insert(symbols, sym);
> > }
> >
> > static struct symbol *symbols__find(struct rb_root_cached *symbols, u64 ip)
> > @@ -554,7 +543,7 @@ void dso__reset_find_symbol_cache(struct dso *dso)
> >
> > void dso__insert_symbol(struct dso *dso, struct symbol *sym)
> > {
> > - __symbols__insert(dso__symbols(dso), sym, dso__kernel(dso));
> > + __symbols__insert(dso__symbols(dso), sym);
> >
> > /* update the symbol cache if necessary */
> > if (dso__last_find_result_addr(dso) >= sym->start &&
> > @@ -716,47 +705,87 @@ int modules__parse(const char *filename, void *arg,
> > return err;
> > }
> >
> > +static int sym_name_cmp(const void *a, const void *b)
> > +{
> > + const char *name = a;
> > + const char *const *sym = b;
> > +
> > + return strcmp(name, *sym);
> > +}
> > +
> > /*
> > * These are symbols in the kernel image, so make sure that
> > * sym is from a kernel DSO.
> > */
> > -static bool symbol__is_idle(const char *name)
> > +bool symbol__is_idle(struct symbol *sym, const struct dso *dso, const struct perf_env *env)
> > {
> > - const char * const idle_symbols[] = {
> > + static const char * const idle_symbols[] = {
> > "acpi_idle_do_entry",
> > "acpi_processor_ffh_cstate_enter",
> > "arch_cpu_idle",
> > "cpu_idle",
> > "cpu_startup_entry",
> > - "idle_cpu",
> > - "intel_idle",
> > - "intel_idle_ibrs",
> > "default_idle",
> > - "native_safe_halt",
> > "enter_idle",
> > "exit_idle",
> > - "mwait_idle",
> > - "mwait_idle_with_hints",
> > - "mwait_idle_with_hints.constprop.0",
> > + "idle_cpu",
> > + "native_safe_halt",
> > "poll_idle",
> > - "ppc64_runlatch_off",
> > "pseries_dedicated_idle_sleep",
> > - "psw_idle",
> > - "psw_idle_exit",
> > - NULL
> > };
> > - int i;
> > - static struct strlist *idle_symbols_list;
> > + const char *name = sym->name;
> > + uint16_t e_machine = env ? env->e_machine : EM_HOST;
> >
> > - if (idle_symbols_list)
> > - return strlist__has_entry(idle_symbols_list, name);
> > + if (sym->idle)
> > + return sym->idle == SYMBOL_IDLE__IDLE;
> >
> > - idle_symbols_list = strlist__new(NULL, NULL);
> > + if (!dso || dso__kernel(dso) == DSO_SPACE__USER) {
> > + sym->idle = SYMBOL_IDLE__NOT_IDLE;
> > + return false;
> > + }
> >
> > - for (i = 0; idle_symbols[i]; i++)
> > - strlist__add(idle_symbols_list, idle_symbols[i]);
> > + /*
> > + * ppc64 uses function descriptors and appends a '.' to the
> > + * start of every instruction address. Remove it.
> > + */
> > + if (name[0] == '.')
> > + name++;
> >
> > - return strlist__has_entry(idle_symbols_list, name);
> > + 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) {
>
> As said in anther thread, intel_idle_irq was still there on my test
> machine. I did a bit debug and found e_machine == 0 so it couldn't run
> into this branch. After dig more, it should be
> deliver_event()->perf_session__find_machine() return a struct machine
> whose env->e_machine is 0. I'm still busy today to do more, wish this
> clue can help.

I can see this, the env's e_machine isn't being lazily initialized for
the host like the arch is. I'll add a patch for this.

Thanks,
Ian

> Thanks,
> Honglei
>
> > + 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;
> > + }
> > +
> > + if (e_machine == EM_S390) {
> > + int major = 0, minor = 0;
> > + const char *release = env && env->os_release
> > + ? env->os_release : perf_version_string;
> > +
> > + sscanf(release, "%d.%d", &major, &minor);
> > +
> > + /* 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 +814,7 @@ 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 c67814d6d6d6..f26f67bd7982 100644
> > --- a/tools/perf/util/symbol.h
> > +++ b/tools/perf/util/symbol.h
> > @@ -25,6 +25,7 @@ struct dso;
> > struct map;
> > struct maps;
> > struct option;
> > +struct perf_env;
> > struct build_id;
> >
> > /*
> > @@ -42,6 +43,12 @@ 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).
> > @@ -57,8 +64,8 @@ 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;
> > /** Resolvable but tools ignore it (e.g. idle routines). */
> > u8 ignore:1;
> > /** Symbol for an inlined function. */
> > @@ -202,8 +209,7 @@ 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);
> > @@ -286,5 +292,6 @@ 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 */
>