Re: [PATCH RESEND] perf lock contention: Account contending locks too

From: Ian Rogers
Date: Tue Feb 27 2024 - 20:14:27 EST

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On Tue, Feb 27, 2024 at 4:31 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Tue, Feb 27, 2024 at 3:49 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
> >
> > On Fri, Feb 9, 2024 at 3:07 PM Namhyung Kim <namhyung@xxxxxxxxxx> 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 <namhyung@xxxxxxxxxx>
> > > ---
> > > 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 31ff19afc20c..d6bafd9a3955 100644
> > > --- a/tools/perf/util/bpf_lock_contention.c
> > > +++ b/tools/perf/util/bpf_lock_contention.c
> > > @@ -179,6 +179,119 @@ 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,
> >
> > It seems strange that this and the raw tracepoint are both test. I see
> > similar non-test uses in libbpf-tools. It would be worth documenting
> > that this isn't test code. Everything else LGTM.
>
> It's a BPF syscall API that allows to run a certain kind of BPF program
> directly and not to necessarily be in a test.

Right, I was meaning that it'd be good to capture that as a comment so
that someone reading the code isn't going to think it is test code.

Thanks,
Ian

> Thanks,
> Namhyung
>
> >
> > > + );
> > > + 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 +301,7 @@ int lock_contention_start(void)
> > > int lock_contention_stop(void)
> > > {
> > > skel->bss->enabled = 0;
> > > + mark_end_timestamp();
> > > return 0;
> > > }
> > >
> > > @@ -301,6 +415,8 @@ 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;
> > > --
> > > 2.43.0.687.g38aa6559b0-goog
> > >

Next message: Thomas Gleixner: "Re: linux-next: duplicate patch in the rcu tree"
Previous message: Jakub Kicinski: "Re: [PATCH] net: make SK_MEMORY_PCPU_RESERV tunable"
In reply to: Namhyung Kim: "Re: [PATCH RESEND] perf lock contention: Account contending locks too"
Next in thread: Namhyung Kim: "Re: [PATCH RESEND] perf lock contention: Account contending locks too"
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