Hello,
On Mon, Oct 21, 2024 at 11:02:00AM +0000, Tengda Wu wrote:
> bperf has a nice ability to share PMUs, but it still does not support
> inherit events during fork(), resulting in some deviations in its stat
> results compared with perf.
>
> perf stat result:
> $ ./perf stat -e cycles,instructions -- ./perf test -w sqrtloop
> Performance counter stats for './perf test -w sqrtloop':
>
> 2,316,038,116 cycles
> 2,859,350,725 instructions
>
> 1.009603637 seconds time elapsed
>
> 1.004196000 seconds user
> 0.003950000 seconds sys
>
> bperf stat result:
> $ ./perf stat --bpf-counters -e cycles,instructions -- \
> ./perf test -w sqrtloop
>
> Performance counter stats for './perf test -w sqrtloop':
>
> 18,762,093 cycles
> 23,487,766 instructions
>
> 1.008913769 seconds time elapsed
>
> 1.003248000 seconds user
> 0.004069000 seconds sys
>
> In order to support event inheritance, two new bpf programs are added
> to monitor the fork and exit of tasks respectively. When a task is
> created, add it to the filter map to enable counting, and reuse the
> `accum_key` of its parent task to count together with the parent task.
> When a task exits, remove it from the filter map to disable counting.
>
> After support:
> $ ./perf stat --bpf-counters -e cycles,instructions -- \
> ./perf test -w sqrtloop
>
> Performance counter stats for './perf test -w sqrtloop':
>
> 2,316,252,189 cycles
> 2,859,946,547 instructions
>
> 1.009422314 seconds time elapsed
>
> 1.003597000 seconds user
> 0.004270000 seconds sys
>
> Signed-off-by: Tengda Wu <wutengda@xxxxxxxxxxxxxxx>
> ---
> tools/perf/builtin-stat.c | 1 +
> tools/perf/util/bpf_counter.c | 35 +++++--
> tools/perf/util/bpf_skel/bperf_follower.bpf.c | 98 +++++++++++++++++--
> tools/perf/util/bpf_skel/bperf_u.h | 5 +
> tools/perf/util/target.h | 1 +
> 5 files changed, 126 insertions(+), 14 deletions(-)
>
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 3e6b9f216e80..8bc880479417 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -2620,6 +2620,7 @@ int cmd_stat(int argc, const char **argv)
> } else if (big_num_opt == 0) /* User passed --no-big-num */
> stat_config.big_num = false;
>
> + target.inherit = !stat_config.no_inherit;
> err = target__validate(&target);
> if (err) {
> target__strerror(&target, err, errbuf, BUFSIZ);
> diff --git a/tools/perf/util/bpf_counter.c b/tools/perf/util/bpf_counter.c
> index 7a8af60e0f51..73fcafbffc6a 100644
> --- a/tools/perf/util/bpf_counter.c
> +++ b/tools/perf/util/bpf_counter.c
> @@ -394,6 +394,7 @@ static int bperf_check_target(struct evsel *evsel,
> }
>
> static struct perf_cpu_map *all_cpu_map;
> +static __u32 filter_entry_cnt;
>
> static int bperf_reload_leader_program(struct evsel *evsel, int attr_map_fd,
> struct perf_event_attr_map_entry *entry)
> @@ -444,12 +445,32 @@ static int bperf_reload_leader_program(struct evsel *evsel, int attr_map_fd,
> return err;
> }
>
> +static int bperf_attach_follower_program(struct bperf_follower_bpf *skel,
> + enum bperf_filter_type filter_type,
> + bool inherit)
> +{
> + struct bpf_link *link;
> + int err = 0;
> +
> + if ((filter_type == BPERF_FILTER_PID ||
> + filter_type == BPERF_FILTER_TGID) && inherit)
> + /* attach all follower bpf progs to enable event inheritance */
> + err = bperf_follower_bpf__attach(skel);
> + else {
> + link = bpf_program__attach(skel->progs.fexit_XXX);
> + if (IS_ERR(link))
> + err = PTR_ERR(link);
> + }
> +
> + return err;
> +}
> +
> static int bperf__load(struct evsel *evsel, struct target *target)
> {
> struct perf_event_attr_map_entry entry = {0xffffffff, 0xffffffff};
> int attr_map_fd, diff_map_fd = -1, err;
> enum bperf_filter_type filter_type;
> - __u32 filter_entry_cnt, i;
> + __u32 i;
>
> if (bperf_check_target(evsel, target, &filter_type, &filter_entry_cnt))
> return -1;
> @@ -529,9 +550,6 @@ static int bperf__load(struct evsel *evsel, struct target *target)
> /* set up reading map */
> bpf_map__set_max_entries(evsel->follower_skel->maps.accum_readings,
> filter_entry_cnt);
> - /* set up follower filter based on target */
> - bpf_map__set_max_entries(evsel->follower_skel->maps.filter,
> - filter_entry_cnt);
> err = bperf_follower_bpf__load(evsel->follower_skel);
> if (err) {
> pr_err("Failed to load follower skeleton\n");
> @@ -543,6 +561,7 @@ static int bperf__load(struct evsel *evsel, struct target *target)
> for (i = 0; i < filter_entry_cnt; i++) {
> int filter_map_fd;
> __u32 key;
> + struct bperf_filter_value fval = { i, 0 };
>
> if (filter_type == BPERF_FILTER_PID ||
> filter_type == BPERF_FILTER_TGID)
> @@ -553,12 +572,14 @@ static int bperf__load(struct evsel *evsel, struct target *target)
> break;
>
> filter_map_fd = bpf_map__fd(evsel->follower_skel->maps.filter);
> - bpf_map_update_elem(filter_map_fd, &key, &i, BPF_ANY);
> + bpf_map_update_elem(filter_map_fd, &key, &fval, BPF_ANY);
> }
>
> evsel->follower_skel->bss->type = filter_type;
> + evsel->follower_skel->bss->inherit = target->inherit;
>
> - err = bperf_follower_bpf__attach(evsel->follower_skel);
> + err = bperf_attach_follower_program(evsel->follower_skel, filter_type,
> + target->inherit);
>
> out:
> if (err && evsel->bperf_leader_link_fd >= 0)
> @@ -623,7 +644,7 @@ static int bperf__read(struct evsel *evsel)
> bperf_sync_counters(evsel);
> reading_map_fd = bpf_map__fd(skel->maps.accum_readings);
>
> - for (i = 0; i < bpf_map__max_entries(skel->maps.accum_readings); i++) {
> + for (i = 0; i < filter_entry_cnt; i++) {
> struct perf_cpu entry;
> __u32 cpu;
>
> diff --git a/tools/perf/util/bpf_skel/bperf_follower.bpf.c b/tools/perf/util/bpf_skel/bperf_follower.bpf.c
> index f193998530d4..0595063139a3 100644
> --- a/tools/perf/util/bpf_skel/bperf_follower.bpf.c
> +++ b/tools/perf/util/bpf_skel/bperf_follower.bpf.c
> @@ -5,6 +5,8 @@
> #include <bpf/bpf_tracing.h>
> #include "bperf_u.h"
>
> +#define MAX_ENTRIES 102400
> +
> struct {
> __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
> __uint(key_size, sizeof(__u32));
> @@ -22,25 +24,29 @@ struct {
> struct {
> __uint(type, BPF_MAP_TYPE_HASH);
> __uint(key_size, sizeof(__u32));
> - __uint(value_size, sizeof(__u32));
> + __uint(value_size, sizeof(struct bperf_filter_value));
> + __uint(max_entries, MAX_ENTRIES);
> + __uint(map_flags, BPF_F_NO_PREALLOC);
> } filter SEC(".maps");
>
> enum bperf_filter_type type = 0;
> int enabled = 0;
> +int inherit;
>
> SEC("fexit/XXX")
> int BPF_PROG(fexit_XXX)
> {
> struct bpf_perf_event_value *diff_val, *accum_val;
> __u32 filter_key, zero = 0;
> - __u32 *accum_key;
> + __u32 accum_key;
> + struct bperf_filter_value *fval;
>
> if (!enabled)
> return 0;
>
> switch (type) {
> case BPERF_FILTER_GLOBAL:
> - accum_key = &zero;
> + accum_key = zero;
> goto do_add;
> case BPERF_FILTER_CPU:
> filter_key = bpf_get_smp_processor_id();
> @@ -49,22 +55,34 @@ int BPF_PROG(fexit_XXX)
> filter_key = bpf_get_current_pid_tgid() & 0xffffffff;
> break;
> case BPERF_FILTER_TGID:
> - filter_key = bpf_get_current_pid_tgid() >> 32;
> + /* Use pid as the filter_key to exclude new task counts
> + * when inherit is disabled. Don't worry about the existing
> + * children in TGID losing their counts, bpf_counter has
> + * already added them to the filter map via perf_thread_map
> + * before this bpf prog runs.
> + */
> + filter_key = inherit ?
> + bpf_get_current_pid_tgid() >> 32 :
> + bpf_get_current_pid_tgid() & 0xffffffff;
I'm not sure why this is needed. Isn't the existing code fine?
Thanks,
Namhyung
> break;
> default:
> return 0;
> }
>
> - accum_key = bpf_map_lookup_elem(&filter, &filter_key);
> - if (!accum_key)
> + fval = bpf_map_lookup_elem(&filter, &filter_key);
> + if (!fval)
> return 0;
>
> + accum_key = fval->accum_key;
> + if (fval->exited)
> + bpf_map_delete_elem(&filter, &filter_key);
> +
> do_add:
> diff_val = bpf_map_lookup_elem(&diff_readings, &zero);
> if (!diff_val)
> return 0;
>
> - accum_val = bpf_map_lookup_elem(&accum_readings, accum_key);
> + accum_val = bpf_map_lookup_elem(&accum_readings, &accum_key);
> if (!accum_val)
> return 0;
>
> @@ -75,4 +93,70 @@ int BPF_PROG(fexit_XXX)
> return 0;
> }
>
> +/* The program is only used for PID or TGID filter types. */
> +SEC("tp_btf/task_newtask")
> +int BPF_PROG(on_newtask, struct task_struct *task, __u64 clone_flags)
> +{
> + __u32 parent_key, child_key;
> + struct bperf_filter_value *parent_fval;
> + struct bperf_filter_value child_fval = { 0 };
> +
> + if (!enabled)
> + return 0;
> +
> + switch (type) {
> + case BPERF_FILTER_PID:
> + parent_key = bpf_get_current_pid_tgid() & 0xffffffff;
> + child_key = task->pid;
> + break;
> + case BPERF_FILTER_TGID:
> + parent_key = bpf_get_current_pid_tgid() >> 32;
> + child_key = task->tgid;
> + if (child_key == parent_key)
> + return 0;
> + break;
> + default:
> + return 0;
> + }
> +
> + /* Check if the current task is one of the target tasks to be counted */
> + parent_fval = bpf_map_lookup_elem(&filter, &parent_key);
> + if (!parent_fval)
> + return 0;
> +
> + /* Start counting for the new task by adding it into filter map,
> + * inherit the accum key of its parent task so that they can be
> + * counted together.
> + */
> + child_fval.accum_key = parent_fval->accum_key;
> + child_fval.exited = 0;
> + bpf_map_update_elem(&filter, &child_key, &child_fval, BPF_NOEXIST);
> +
> + return 0;
> +}
> +
> +/* The program is only used for PID or TGID filter types. */
> +SEC("tp_btf/sched_process_exit")
> +int BPF_PROG(on_exittask, struct task_struct *task)
> +{
> + __u32 pid;
> + struct bperf_filter_value *fval;
> +
> + if (!enabled)
> + return 0;
> +
> + /* Stop counting for this task by removing it from filter map.
> + * For TGID type, if the pid can be found in the map, it means that
> + * this pid belongs to the leader task. After the task exits, the
> + * tgid of its child tasks (if any) will be 1, so the pid can be
> + * safely removed.
> + */
> + pid = task->pid;
> + fval = bpf_map_lookup_elem(&filter, &pid);
> + if (fval)
> + fval->exited = 1;
> +
> + return 0;
> +}
> +
> char LICENSE[] SEC("license") = "Dual BSD/GPL";
> diff --git a/tools/perf/util/bpf_skel/bperf_u.h b/tools/perf/util/bpf_skel/bperf_u.h
> index 1ce0c2c905c1..4a4a753980be 100644
> --- a/tools/perf/util/bpf_skel/bperf_u.h
> +++ b/tools/perf/util/bpf_skel/bperf_u.h
> @@ -11,4 +11,9 @@ enum bperf_filter_type {
> BPERF_FILTER_TGID,
> };
>
> +struct bperf_filter_value {
> + __u32 accum_key;
> + __u8 exited;
> +};
> +
> #endif /* __BPERF_STAT_U_H */
> diff --git a/tools/perf/util/target.h b/tools/perf/util/target.h
> index d582cae8e105..2ee2cc30340f 100644
> --- a/tools/perf/util/target.h
> +++ b/tools/perf/util/target.h
> @@ -17,6 +17,7 @@ struct target {
> bool default_per_cpu;
> bool per_thread;
> bool use_bpf;
> + bool inherit;
> int initial_delay;
> const char *attr_map;
> };
> --
> 2.34.1
>
