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Message-ID: <20240228053335.312776-1-namhyung@kernel.org>
Date: Tue, 27 Feb 2024 21:33:35 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>,
Ian Rogers <irogers@...gle.com>
Cc: Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
linux-perf-users@...r.kernel.org,
Song Liu <song@...nel.org>,
bpf@...r.kernel.org
Subject: [PATCH v2] perf lock contention: Account contending locks too
Currently it accounts the contention using delta between timestamps in
lock:contention_begin and lock:contention_end tracepoints. But it means
the lock should see the both events during the monitoring period.
Actually there are 4 cases that happen with the monitoring:
monitoring period
/ \
| |
1: B------+-----------------------+--------E
2: B----+-------------E |
3: | B-----------+----E
4: | B-------------E |
| |
t0 t1
where B and E mean contention BEGIN and END, respectively. So it only
accounts the case 4 for now. It seems there's no way to handle the case
1. The case 2 might be handled if it saved the timestamp (t0), but it
lacks the information from the B notably the flags which shows the lock
types. Also it could be a nested lock which it currently ignores. So
I think we should ignore the case 2.
However we can handle the case 3 if we save the timestamp (t1) at the
end of the period. And then it can iterate the map entries in the
userspace and update the lock stat accordinly.
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
v2: add a comment on mark_end_timestamp (Ian)
tools/perf/util/bpf_lock_contention.c | 120 ++++++++++++++++++
.../perf/util/bpf_skel/lock_contention.bpf.c | 16 ++-
tools/perf/util/bpf_skel/lock_data.h | 7 +
3 files changed, 136 insertions(+), 7 deletions(-)
diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index 31ff19afc20c..9af76c6b2543 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -179,6 +179,123 @@ int lock_contention_prepare(struct lock_contention *con)
return 0;
}
+/*
+ * Run the BPF program directly using BPF_PROG_TEST_RUN to update the end
+ * timestamp in ktime so that it can calculate delta easily.
+ */
+static void mark_end_timestamp(void)
+{
+ DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts,
+ .flags = BPF_F_TEST_RUN_ON_CPU,
+ );
+ int prog_fd = bpf_program__fd(skel->progs.end_timestamp);
+
+ bpf_prog_test_run_opts(prog_fd, &opts);
+}
+
+static void update_lock_stat(int map_fd, int pid, u64 end_ts,
+ enum lock_aggr_mode aggr_mode,
+ struct tstamp_data *ts_data)
+{
+ u64 delta;
+ struct contention_key stat_key = {};
+ struct contention_data stat_data;
+
+ if (ts_data->timestamp >= end_ts)
+ return;
+
+ delta = end_ts - ts_data->timestamp;
+
+ switch (aggr_mode) {
+ case LOCK_AGGR_CALLER:
+ stat_key.stack_id = ts_data->stack_id;
+ break;
+ case LOCK_AGGR_TASK:
+ stat_key.pid = pid;
+ break;
+ case LOCK_AGGR_ADDR:
+ stat_key.lock_addr_or_cgroup = ts_data->lock;
+ break;
+ case LOCK_AGGR_CGROUP:
+ /* TODO */
+ return;
+ default:
+ return;
+ }
+
+ if (bpf_map_lookup_elem(map_fd, &stat_key, &stat_data) < 0)
+ return;
+
+ stat_data.total_time += delta;
+ stat_data.count++;
+
+ if (delta > stat_data.max_time)
+ stat_data.max_time = delta;
+ if (delta < stat_data.min_time)
+ stat_data.min_time = delta;
+
+ bpf_map_update_elem(map_fd, &stat_key, &stat_data, BPF_EXIST);
+}
+
+/*
+ * Account entries in the tstamp map (which didn't see the corresponding
+ * lock:contention_end tracepoint) using end_ts.
+ */
+static void account_end_timestamp(struct lock_contention *con)
+{
+ int ts_fd, stat_fd;
+ int *prev_key, key;
+ u64 end_ts = skel->bss->end_ts;
+ int total_cpus;
+ enum lock_aggr_mode aggr_mode = con->aggr_mode;
+ struct tstamp_data ts_data, *cpu_data;
+
+ /* Iterate per-task tstamp map (key = TID) */
+ ts_fd = bpf_map__fd(skel->maps.tstamp);
+ stat_fd = bpf_map__fd(skel->maps.lock_stat);
+
+ prev_key = NULL;
+ while (!bpf_map_get_next_key(ts_fd, prev_key, &key)) {
+ if (bpf_map_lookup_elem(ts_fd, &key, &ts_data) == 0) {
+ int pid = key;
+
+ if (aggr_mode == LOCK_AGGR_TASK && con->owner)
+ pid = ts_data.flags;
+
+ update_lock_stat(stat_fd, pid, end_ts, aggr_mode,
+ &ts_data);
+ }
+
+ prev_key = &key;
+ }
+
+ /* Now it'll check per-cpu tstamp map which doesn't have TID. */
+ if (aggr_mode == LOCK_AGGR_TASK || aggr_mode == LOCK_AGGR_CGROUP)
+ return;
+
+ total_cpus = cpu__max_cpu().cpu;
+ ts_fd = bpf_map__fd(skel->maps.tstamp_cpu);
+
+ cpu_data = calloc(total_cpus, sizeof(*cpu_data));
+ if (cpu_data == NULL)
+ return;
+
+ prev_key = NULL;
+ while (!bpf_map_get_next_key(ts_fd, prev_key, &key)) {
+ if (bpf_map_lookup_elem(ts_fd, &key, cpu_data) < 0)
+ goto next;
+
+ for (int i = 0; i < total_cpus; i++) {
+ update_lock_stat(stat_fd, -1, end_ts, aggr_mode,
+ &cpu_data[i]);
+ }
+
+next:
+ prev_key = &key;
+ }
+ free(cpu_data);
+}
+
int lock_contention_start(void)
{
skel->bss->enabled = 1;
@@ -188,6 +305,7 @@ int lock_contention_start(void)
int lock_contention_stop(void)
{
skel->bss->enabled = 0;
+ mark_end_timestamp();
return 0;
}
@@ -301,6 +419,8 @@ int lock_contention_read(struct lock_contention *con)
if (stack_trace == NULL)
return -1;
+ account_end_timestamp(con);
+
if (con->aggr_mode == LOCK_AGGR_TASK) {
struct thread *idle = __machine__findnew_thread(machine,
/*pid=*/0,
diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
index 95cd8414f6ef..fb54bd38e7d0 100644
--- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
+++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
@@ -19,13 +19,6 @@
#define LCB_F_PERCPU (1U << 4)
#define LCB_F_MUTEX (1U << 5)
-struct tstamp_data {
- __u64 timestamp;
- __u64 lock;
- __u32 flags;
- __s32 stack_id;
-};
-
/* callstack storage */
struct {
__uint(type, BPF_MAP_TYPE_STACK_TRACE);
@@ -140,6 +133,8 @@ int perf_subsys_id = -1;
/* determine the key of lock stat */
int aggr_mode;
+__u64 end_ts;
+
/* error stat */
int task_fail;
int stack_fail;
@@ -559,4 +554,11 @@ int BPF_PROG(collect_lock_syms)
return 0;
}
+SEC("raw_tp/bpf_test_finish")
+int BPF_PROG(end_timestamp)
+{
+ end_ts = bpf_ktime_get_ns();
+ return 0;
+}
+
char LICENSE[] SEC("license") = "Dual BSD/GPL";
diff --git a/tools/perf/util/bpf_skel/lock_data.h b/tools/perf/util/bpf_skel/lock_data.h
index 08482daf61be..36af11faad03 100644
--- a/tools/perf/util/bpf_skel/lock_data.h
+++ b/tools/perf/util/bpf_skel/lock_data.h
@@ -3,6 +3,13 @@
#ifndef UTIL_BPF_SKEL_LOCK_DATA_H
#define UTIL_BPF_SKEL_LOCK_DATA_H
+struct tstamp_data {
+ u64 timestamp;
+ u64 lock;
+ u32 flags;
+ u32 stack_id;
+};
+
struct contention_key {
u32 stack_id;
u32 pid;
--
2.44.0.rc1.240.g4c46232300-goog
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