[PATCH 3/4] perf lock contention: Support filters for different aggregation

Namhyung Kim
2023-02-02T05:05:20Z

It'd be useful to filter other than the current aggregation mode. For
example, users may want to see callstacks for specific locks only. Or
they may want tasks from a certain callstack.

The tracepoints already collected the information but it needs to check
the condition again when processing the event. And it needs to change
BPF to allow the key combinations.

The lock contentions on 'rcu_state' spinlock can be monitored:

$ sudo perf lock con -abv -L rcu_state sleep 1
...
contended total wait max wait avg wait type caller

4 151.39 us 62.57 us 37.85 us spinlock rcu_core+0xcb
0xffffffff81fd1666 _raw_spin_lock_irqsave+0x46
0xffffffff8172d76b rcu_core+0xcb
0xffffffff822000eb __softirqentry_text_start+0xeb
0xffffffff816a0ba9 __irq_exit_rcu+0xc9
0xffffffff81fc0112 sysvec_apic_timer_interrupt+0xa2
0xffffffff82000e46 asm_sysvec_apic_timer_interrupt+0x16
0xffffffff81d49f78 cpuidle_enter_state+0xd8
0xffffffff81d4a259 cpuidle_enter+0x29
1 30.21 us 30.21 us 30.21 us spinlock rcu_core+0xcb
0xffffffff81fd1666 _raw_spin_lock_irqsave+0x46
0xffffffff8172d76b rcu_core+0xcb
0xffffffff822000eb __softirqentry_text_start+0xeb
0xffffffff816a0ba9 __irq_exit_rcu+0xc9
0xffffffff81fc00c4 sysvec_apic_timer_interrupt+0x54
0xffffffff82000e46 asm_sysvec_apic_timer_interrupt+0x16
1 28.84 us 28.84 us 28.84 us spinlock rcu_accelerate_cbs_unlocked+0x40
0xffffffff81fd1c60 _raw_spin_lock+0x30
0xffffffff81728cf0 rcu_accelerate_cbs_unlocked+0x40
0xffffffff8172da82 rcu_core+0x3e2
0xffffffff822000eb __softirqentry_text_start+0xeb
0xffffffff816a0ba9 __irq_exit_rcu+0xc9
0xffffffff81fc0112 sysvec_apic_timer_interrupt+0xa2
0xffffffff82000e46 asm_sysvec_apic_timer_interrupt+0x16
0xffffffff81d49f78 cpuidle_enter_state+0xd8
...

To see tasks calling 'rcu_core' function:

$ sudo perf lock con -abt -S rcu_core sleep 1
contended total wait max wait avg wait pid comm

19 23.46 us 2.21 us 1.23 us 0 swapper
2 18.37 us 17.01 us 9.19 us 2061859 ThreadPoolForeg
3 5.76 us 1.97 us 1.92 us 3909 pipewire-pulse
1 2.26 us 2.26 us 2.26 us 1809271 MediaSu~isor #2
1 1.97 us 1.97 us 1.97 us 1514882 Chrome_ChildIOT
1 987 ns 987 ns 987 ns 3740 pipewire-pulse

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/builtin-lock.c | 75 +++++++++++--------
tools/perf/util/bpf_lock_contention.c | 44 +++++++----
.../perf/util/bpf_skel/lock_contention.bpf.c | 15 ++--
tools/perf/util/bpf_skel/lock_data.h | 4 +-
tools/perf/util/lock-contention.h | 2 +
5 files changed, 89 insertions(+), 51 deletions(-)

diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
index 0593c6e636c6..0d11f301fd72 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -509,6 +509,34 @@ struct lock_stat *lock_stat_findnew(u64 addr, const char *name, int flags)
return NULL;
}

+bool match_callstack_filter(struct machine *machine, u64 *callstack)
+{
+ struct map *kmap;
+ struct symbol *sym;
+ u64 ip;
+
+ if (list_empty(&callstack_filters))
+ return true;
+
+ for (int i = 0; i < max_stack_depth; i++) {
+ struct callstack_filter *filter;
+
+ if (!callstack || !callstack[i])
+ break;
+
+ ip = callstack[i];
+ sym = machine__find_kernel_symbol(machine, ip, &kmap);
+ if (sym == NULL)
+ continue;
+
+ list_for_each_entry(filter, &callstack_filters, list) {
+ if (strstr(sym->name, filter->name))
+ return true;
+ }
+ }
+ return false;
+}
+
struct trace_lock_handler {
/* it's used on CONFIG_LOCKDEP */
int (*acquire_event)(struct evsel *evsel,
@@ -1070,12 +1098,6 @@ static int report_lock_contention_begin_event(struct evsel *evsel,
ls = lock_stat_findnew(key, name, flags);
if (!ls)
return -ENOMEM;
-
- if (aggr_mode == LOCK_AGGR_CALLER && needs_callstack()) {
- ls->callstack = get_callstack(sample, max_stack_depth);
- if (ls->callstack == NULL)
- return -ENOMEM;
- }
}

if (filters.nr_types) {
@@ -1106,6 +1128,22 @@ static int report_lock_contention_begin_event(struct evsel *evsel,
return 0;
}

+ if (needs_callstack()) {
+ u64 *callstack = get_callstack(sample, max_stack_depth);
+ if (callstack == NULL)
+ return -ENOMEM;
+
+ if (!match_callstack_filter(machine, callstack)) {
+ free(callstack);
+ return 0;
+ }
+
+ if (ls->callstack == NULL)
+ ls->callstack = callstack;
+ else
+ free(callstack);
+ }
+
ts = thread_stat_findnew(sample->tid);
if (!ts)
return -ENOMEM;
@@ -1606,31 +1644,6 @@ static void print_contention_result(struct lock_contention *con)
if (!st->wait_time_total)
continue;

- if (aggr_mode == LOCK_AGGR_CALLER && !list_empty(&callstack_filters)) {
- struct map *kmap;
- struct symbol *sym;
- u64 ip;
-
- for (int i = 0; i < max_stack_depth; i++) {
- struct callstack_filter *filter;
-
- if (!st->callstack || !st->callstack[i])
- break;
-
- ip = st->callstack[i];
- sym = machine__find_kernel_symbol(con->machine, ip, &kmap);
- if (sym == NULL)
- continue;
-
- list_for_each_entry(filter, &callstack_filters, list) {
- if (strstr(sym->name, filter->name))
- goto found;
- }
- }
- continue;
- }
-
-found:
list_for_each_entry(key, &lock_keys, list) {
key->print(key, st);
pr_info(" ");
diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index c6f2db603d5a..3b4308b7b6bf 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -34,13 +34,15 @@ int lock_contention_prepare(struct lock_contention *con)
bpf_map__set_max_entries(skel->maps.lock_stat, con->map_nr_entries);
bpf_map__set_max_entries(skel->maps.tstamp, con->map_nr_entries);

- if (con->aggr_mode == LOCK_AGGR_TASK) {
+ if (con->aggr_mode == LOCK_AGGR_TASK)
bpf_map__set_max_entries(skel->maps.task_data, con->map_nr_entries);
- bpf_map__set_max_entries(skel->maps.stacks, 1);
- } else {
+ else
bpf_map__set_max_entries(skel->maps.task_data, 1);
+
+ if (con->save_callstack)
bpf_map__set_max_entries(skel->maps.stacks, con->map_nr_entries);
- }
+ else
+ bpf_map__set_max_entries(skel->maps.stacks, 1);

if (target__has_cpu(target))
ncpus = perf_cpu_map__nr(evlist->core.user_requested_cpus);
@@ -146,6 +148,7 @@ int lock_contention_prepare(struct lock_contention *con)
/* these don't work well if in the rodata section */
skel->bss->stack_skip = con->stack_skip;
skel->bss->aggr_mode = con->aggr_mode;
+ skel->bss->needs_callstack = con->save_callstack;

lock_contention_bpf__attach(skel);
return 0;
@@ -178,7 +181,7 @@ static const char *lock_contention_get_name(struct lock_contention *con,
if (con->aggr_mode == LOCK_AGGR_TASK) {
struct contention_task_data task;
struct thread *t;
- int pid = key->aggr_key;
+ int pid = key->pid;
int task_fd = bpf_map__fd(skel->maps.task_data);

/* do not update idle comm which contains CPU number */
@@ -192,7 +195,7 @@ static const char *lock_contention_get_name(struct lock_contention *con,
}

if (con->aggr_mode == LOCK_AGGR_ADDR) {
- sym = machine__find_kernel_symbol(machine, key->aggr_key, &kmap);
+ sym = machine__find_kernel_symbol(machine, key->lock_addr, &kmap);
if (sym)
name = sym->name;
return name;
@@ -253,20 +256,35 @@ int lock_contention_read(struct lock_contention *con)

prev_key = NULL;
while (!bpf_map_get_next_key(fd, prev_key, &key)) {
- s32 stack_id;
+ s64 ls_key;
const char *name;

/* to handle errors in the loop body */
err = -1;

bpf_map_lookup_elem(fd, &key, &data);
-
if (con->save_callstack) {
- stack_id = key.aggr_key;
- bpf_map_lookup_elem(stack, &stack_id, stack_trace);
+ bpf_map_lookup_elem(stack, &key.stack_id, stack_trace);
+
+ if (!match_callstack_filter(machine, stack_trace))
+ goto next;
}

- st = lock_stat_find(key.aggr_key);
+ switch (con->aggr_mode) {
+ case LOCK_AGGR_CALLER:
+ ls_key = key.stack_id;
+ break;
+ case LOCK_AGGR_TASK:
+ ls_key = key.pid;
+ break;
+ case LOCK_AGGR_ADDR:
+ ls_key = key.lock_addr;
+ break;
+ default:
+ goto next;
+ }
+
+ st = lock_stat_find(ls_key);
if (st != NULL) {
st->wait_time_total += data.total_time;
if (st->wait_time_max < data.max_time)
@@ -281,7 +299,7 @@ int lock_contention_read(struct lock_contention *con)
}

name = lock_contention_get_name(con, &key, stack_trace);
- st = lock_stat_findnew(key.aggr_key, name, data.flags);
+ st = lock_stat_findnew(ls_key, name, data.flags);
if (st == NULL)
break;

@@ -293,8 +311,6 @@ int lock_contention_read(struct lock_contention *con)
if (data.count)
st->avg_wait_time = data.total_time / data.count;

- st->flags = data.flags;
-
if (con->save_callstack) {
st->callstack = memdup(stack_trace, stack_size);
if (st->callstack == NULL)
diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
index ad0ca5d50557..7ce276ed987e 100644
--- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
+++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
@@ -82,6 +82,7 @@ int has_cpu;
int has_task;
int has_type;
int has_addr;
+int needs_callstack;
int stack_skip;

/* determine the key of lock stat */
@@ -173,7 +174,7 @@ int contention_begin(u64 *ctx)
pelem->lock = (__u64)ctx[0];
pelem->flags = (__u32)ctx[1];

- if (aggr_mode == LOCK_AGGR_CALLER) {
+ if (needs_callstack) {
pelem->stack_id = bpf_get_stackid(ctx, &stacks,
BPF_F_FAST_STACK_CMP | stack_skip);
if (pelem->stack_id < 0)
@@ -188,7 +189,7 @@ int contention_end(u64 *ctx)
{
__u32 pid;
struct tstamp_data *pelem;
- struct contention_key key;
+ struct contention_key key = {};
struct contention_data *data;
__u64 duration;

@@ -204,14 +205,18 @@ int contention_end(u64 *ctx)

switch (aggr_mode) {
case LOCK_AGGR_CALLER:
- key.aggr_key = pelem->stack_id;
+ key.stack_id = pelem->stack_id;
break;
case LOCK_AGGR_TASK:
- key.aggr_key = pid;
+ key.pid = pid;
update_task_data(pid);
+ if (needs_callstack)
+ key.stack_id = pelem->stack_id;
break;
case LOCK_AGGR_ADDR:
- key.aggr_key = pelem->lock;
+ key.lock_addr = pelem->lock;
+ if (needs_callstack)
+ key.stack_id = pelem->stack_id;
break;
default:
/* should not happen */
diff --git a/tools/perf/util/bpf_skel/lock_data.h b/tools/perf/util/bpf_skel/lock_data.h
index ce71cf1a7e1e..3d35fd4407ac 100644
--- a/tools/perf/util/bpf_skel/lock_data.h
+++ b/tools/perf/util/bpf_skel/lock_data.h
@@ -4,7 +4,9 @@
#define UTIL_BPF_SKEL_LOCK_DATA_H

struct contention_key {
- u64 aggr_key; /* can be stack_id, pid or lock addr */
+ u32 stack_id;
+ u32 pid;
+ u64 lock_addr;
};

#define TASK_COMM_LEN 16
diff --git a/tools/perf/util/lock-contention.h b/tools/perf/util/lock-contention.h
index 39d5bfc77f4e..e5fc036108ec 100644
--- a/tools/perf/util/lock-contention.h
+++ b/tools/perf/util/lock-contention.h
@@ -68,6 +68,8 @@ struct lock_stat {
struct lock_stat *lock_stat_find(u64 addr);
struct lock_stat *lock_stat_findnew(u64 addr, const char *name, int flags);

+bool match_callstack_filter(struct machine *machine, u64 *callstack);
+
/*
* struct lock_seq_stat:
* Place to put on state of one lock sequence
--
2.39.1.456.gfc5497dd1b-goog