[PATCH 1/4] perf lock contention: Factor out lock_contention_get_name()

Namhyung Kim
2023-02-02T05:05:09Z

The lock_contention_get_name() returns a name for the lock stat entry
based on the current aggregation mode. As it's called sequentially in a
single thread, it can return the address of a static buffer for symbol
and offset of the caller.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/util/bpf_lock_contention.c | 113 ++++++++++++++------------
1 file changed, 63 insertions(+), 50 deletions(-)

diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index 4902ac331f41..967ce168f163 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -163,9 +163,68 @@ int lock_contention_stop(void)
return 0;
}

+static const char *lock_contention_get_name(struct lock_contention *con,
+ struct contention_key *key,
+ u64 *stack_trace)
+{
+ int idx = 0;
+ u64 addr;
+ const char *name = "";
+ static char name_buf[KSYM_NAME_LEN];
+ struct symbol *sym;
+ struct map *kmap;
+ struct machine *machine = con->machine;
+
+ if (con->aggr_mode == LOCK_AGGR_TASK) {
+ struct contention_task_data task;
+ struct thread *t;
+ int pid = key->aggr_key;
+ int task_fd = bpf_map__fd(skel->maps.task_data);
+
+ /* do not update idle comm which contains CPU number */
+ if (pid) {
+ bpf_map_lookup_elem(task_fd, &pid, &task);
+ t = __machine__findnew_thread(machine, /*pid=*/-1, pid);
+ thread__set_comm(t, task.comm, /*timestamp=*/0);
+ name = task.comm;
+ }
+ return name;
+ }
+
+ if (con->aggr_mode == LOCK_AGGR_ADDR) {
+ sym = machine__find_kernel_symbol(machine, key->aggr_key, &kmap);
+ if (sym)
+ name = sym->name;
+ return name;
+ }
+
+ /* LOCK_AGGR_CALLER: skip lock internal functions */
+ while (machine__is_lock_function(machine, stack_trace[idx]) &&
+ idx < con->max_stack - 1)
+ idx++;
+
+ addr = stack_trace[idx];
+ sym = machine__find_kernel_symbol(machine, addr, &kmap);
+
+ if (sym) {
+ unsigned long offset;
+
+ offset = kmap->map_ip(kmap, addr) - sym->start;
+
+ if (offset == 0)
+ return sym->name;
+
+ snprintf(name_buf, sizeof(name_buf), "%s+%#lx", sym->name, offset);
+ } else {
+ snprintf(name_buf, sizeof(name_buf), "%#lx", (unsigned long)addr);
+ }
+
+ return name_buf;
+}
+
int lock_contention_read(struct lock_contention *con)
{
- int fd, stack, task_fd, err = 0;
+ int fd, stack, err = 0;
struct contention_key *prev_key, key;
struct contention_data data = {};
struct lock_stat *st = NULL;
@@ -175,7 +234,6 @@ int lock_contention_read(struct lock_contention *con)

fd = bpf_map__fd(skel->maps.lock_stat);
stack = bpf_map__fd(skel->maps.stacks);
- task_fd = bpf_map__fd(skel->maps.task_data);

con->lost = skel->bss->lost;

@@ -195,9 +253,6 @@ int lock_contention_read(struct lock_contention *con)

prev_key = NULL;
while (!bpf_map_get_next_key(fd, prev_key, &key)) {
- struct map *kmap;
- struct symbol *sym;
- int idx = 0;
s32 stack_id;

/* to handle errors in the loop body */
@@ -219,61 +274,19 @@ int lock_contention_read(struct lock_contention *con)
st->flags = data.flags;
st->addr = key.aggr_key;

- if (con->aggr_mode == LOCK_AGGR_TASK) {
- struct contention_task_data task;
- struct thread *t;
- int pid = key.aggr_key;
-
- /* do not update idle comm which contains CPU number */
- if (st->addr) {
- bpf_map_lookup_elem(task_fd, &pid, &task);
- t = __machine__findnew_thread(machine, /*pid=*/-1, pid);
- thread__set_comm(t, task.comm, /*timestamp=*/0);
- }
- goto next;
- }
-
- if (con->aggr_mode == LOCK_AGGR_ADDR) {
- sym = machine__find_kernel_symbol(machine, st->addr, &kmap);
- if (sym)
- st->name = strdup(sym->name);
- goto next;
- }
-
stack_id = key.aggr_key;
bpf_map_lookup_elem(stack, &stack_id, stack_trace);

- /* skip lock internal functions */
- while (machine__is_lock_function(machine, stack_trace[idx]) &&
- idx < con->max_stack - 1)
- idx++;
-
- st->addr = stack_trace[idx];
- sym = machine__find_kernel_symbol(machine, st->addr, &kmap);
-
- if (sym) {
- unsigned long offset;
- int ret = 0;
-
- offset = kmap->map_ip(kmap, st->addr) - sym->start;
-
- if (offset)
- ret = asprintf(&st->name, "%s+%#lx", sym->name, offset);
- else
- st->name = strdup(sym->name);
-
- if (ret < 0 || st->name == NULL)
- break;
- } else if (asprintf(&st->name, "%#lx", (unsigned long)st->addr) < 0) {
+ st->name = strdup(lock_contention_get_name(con, &key, stack_trace));
+ if (st->name == NULL)
break;
- }

if (con->save_callstack) {
st->callstack = memdup(stack_trace, stack_size);
if (st->callstack == NULL)
break;
}
-next:
+
hlist_add_head(&st->hash_entry, con->result);
prev_key = &key;

--
2.39.1.456.gfc5497dd1b-goog