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

Ian Rogers
2026-03-25T16:18:47Z

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) {
+ 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 */
--
2.53.0.1018.g2bb0e51243-goog