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 <[email protected]>
---
tools/perf/util/bpf_lock_contention.c | 116 ++++++++++++++++++
.../perf/util/bpf_skel/lock_contention.bpf.c | 16 +--
tools/perf/util/bpf_skel/lock_data.h | 7 ++
3 files changed, 132 insertions(+), 7 deletions(-)
diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index e105245eb905..2476459bf2ef 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -178,6 +178,119 @@ int lock_contention_prepare(struct lock_contention *con)
return 0;
}
+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;
@@ -187,6 +300,7 @@ int lock_contention_start(void)
int lock_contention_stop(void)
{
skel->bss->enabled = 0;
+ mark_end_timestamp();
return 0;
}
@@ -300,6 +414,8 @@ 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;
--
2.43.0.472.g3155946c3a-goog
Ping!
On Thu, Dec 7, 2023 at 6:28 PM Namhyung Kim <[email protected]> wrote:
>
> 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 <[email protected]>
> ---
> tools/perf/util/bpf_lock_contention.c | 116 ++++++++++++++++++
> .../perf/util/bpf_skel/lock_contention.bpf.c | 16 +--
> tools/perf/util/bpf_skel/lock_data.h | 7 ++
> 3 files changed, 132 insertions(+), 7 deletions(-)
>
> diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
> index e105245eb905..2476459bf2ef 100644
> --- a/tools/perf/util/bpf_lock_contention.c
> +++ b/tools/perf/util/bpf_lock_contention.c
> @@ -178,6 +178,119 @@ int lock_contention_prepare(struct lock_contention *con)
> return 0;
> }
>
> +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;
> @@ -187,6 +300,7 @@ int lock_contention_start(void)
> int lock_contention_stop(void)
> {
> skel->bss->enabled = 0;
> + mark_end_timestamp();
> return 0;
> }
>
> @@ -300,6 +414,8 @@ 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;
> --
> 2.43.0.472.g3155946c3a-goog
>