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

Ian Rogers
2026-03-24T17:14:18Z

On Mon, Mar 2, 2026 at 3:43 PM Ian Rogers <irogers@google.com> 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/
>
> Signed-off-by: Ian Rogers <irogers@google.com>

Ping.

Thanks,
Ian

> ---
> tools/perf/builtin-top.c | 6 +-
> tools/perf/util/symbol-elf.c | 2 +-
> tools/perf/util/symbol.c | 106 ++++++++++++++++++++++-------------
> tools/perf/util/symbol.h | 15 +++--
> 4 files changed, 85 insertions(+), 44 deletions(-)
>
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index 710604c4f6f6..bc3c8e3b6ec0 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -750,6 +750,7 @@ 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;
> @@ -829,7 +830,10 @@ 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 76912c62b6a0..6bb46384aa0c 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1725,7 +1725,7 @@ 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 8662001e1e25..6155f509ca70 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 "debug.h"
> #include "event.h"
> @@ -51,7 +53,6 @@
>
> 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 +705,88 @@ 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 (sym->idle)
> + return sym->idle == SYMBOL_IDLE__IDLE;
> +
> + if (!dso || dso__kernel(dso) == DSO_SPACE__USER) {
> + sym->idle = SYMBOL_IDLE__NOT_IDLE;
> + return false;
> + }
>
> - 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] == '.')
> + 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) {
> + 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;
> /** 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
>