Re: [PATCH -next v2 1/2] perf stat: Support inherit events during fork() for bperf

From: Tengda Wu
Date: Sun Sep 15 2024 - 07:23:05 EST

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In reply to: Namhyung Kim: "Re: [PATCH -next v2 1/2] perf stat: Support inherit events during fork() for bperf"
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On 2024/9/15 2:02, Namhyung Kim wrote:
> Hello,
>
> On Thu, Sep 05, 2024 at 11:59:17AM +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 # 1.23 insn per cycle
>>
>> 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 # 1.25 insn per cycle
>>
>> 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':
>>
>> 2,316,543,537 cycles
>> 2,859,677,779 instructions # 1.23 insn per cycle
>>
>> 1.009566332 seconds time elapsed
>>
>> 1.004414000 seconds user
>> 0.003545000 seconds sys
>>
>> Signed-off-by: Tengda Wu <wutengda@xxxxxxxxxxxxxxx>
>> ---
>> tools/perf/util/bpf_counter.c | 32 +++++++--
>> tools/perf/util/bpf_skel/bperf_follower.bpf.c | 70 +++++++++++++++++--
>> tools/perf/util/bpf_skel/bperf_u.h | 5 ++
>> 3 files changed, 94 insertions(+), 13 deletions(-)
>>
>> diff --git a/tools/perf/util/bpf_counter.c b/tools/perf/util/bpf_counter.c
>> index 7a8af60e0f51..94aa46f50052 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 +445,31 @@ static int bperf_reload_leader_program(struct evsel *evsel, int attr_map_fd,
>> return err;
>> }
>>
>> +/* Attach programs on demand according to filter types to reduce overhead */
>> +static int bperf_attach_follower_program(struct bperf_follower_bpf *skel,
>> + enum bperf_filter_type filter_type)
>> +{
>> + struct bpf_link *link;
>> + int err = 0;
>> +
>> + if (filter_type == BPERF_FILTER_PID ||
>> + filter_type == BPERF_FILTER_TGID)
>> + 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 +549,6 @@ 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 +560,7 @@ 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 +571,12 @@ 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;
>>
>> - err = bperf_follower_bpf__attach(evsel->follower_skel);
>> + err = bperf_attach_follower_program(evsel->follower_skel, filter_type);
>>
>> out:
>> if (err && evsel->bperf_leader_link_fd >= 0)
>> @@ -623,7 +641,7 @@ 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..32b944f28776 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));
>> @@ -22,7 +24,9 @@ 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;
>> @@ -33,14 +37,15 @@ 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();
>> @@ -55,16 +60,20 @@ int BPF_PROG(fexit_XXX)
>> 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 +84,53 @@ 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_pid, child_pid;
>> + struct bperf_filter_value *parent_fval;
>> + struct bperf_filter_value child_fval = { 0 };
>> +
>> + if (!enabled)
>> + return 0;
>> +
>> + parent_pid = bpf_get_current_pid_tgid() >> 32;
>> + child_pid = task->pid;
>
> Should it use pid or tgid depending on the filter type?
>
> Thanks,
> Namhyung

Oh, it should. I just find two issues here:
One is that the task pid added under the TGID type will not be used by sched_switch prog,
causing memory waste in map.
Another is that using tgid to search for tasks under the PID type may find nothing, which
would miss some child task counts.

I'll fix them in the next version.

Thank you for pointing this out.
Tengda

>
>> +
>> + /* Check if the current task is one of the target tasks to be counted */
>> + parent_fval = bpf_map_lookup_elem(&filter, &parent_pid);
>> + 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_pid, &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 */
>> + 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 */
>> --
>> 2.34.1
>>

Next message: Chen-Yu Tsai: "Re: [PATCH v7 06/10] i2c: Introduce OF component probe function"
Previous message: Josh Poimboeuf: "Re: [PATCH v2 00/11] unwind, perf: sframe user space unwinding, deferred perf callchains"
In reply to: Namhyung Kim: "Re: [PATCH -next v2 1/2] perf stat: Support inherit events during fork() for bperf"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]