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Message-ID: <9570ce3e-5372-48b3-beca-ea251431326b@huaweicloud.com>
Date: Thu, 5 Sep 2024 14:44:14 +0800
From: Tengda Wu <wutengda@...weicloud.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>, kan.liang@...ux.intel.com,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
bpf@...r.kernel.org, Song Liu <song@...nel.org>
Subject: Re: [PATCH -next 1/2] perf stat: Support inherit events during fork()
for bperf
On 2024/9/5 12:01, Namhyung Kim wrote:
> Hello,
>
> On Wed, Sep 04, 2024 at 12:31:02PM +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.
>
> Right, I think we may need this for other BPF programs.
>
>>
>> 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@...weicloud.com>
>> ---
>> tools/perf/util/bpf_counter.c | 9 +--
>> tools/perf/util/bpf_skel/bperf_follower.bpf.c | 75 +++++++++++++++++--
>> tools/perf/util/bpf_skel/bperf_u.h | 5 ++
>> 3 files changed, 78 insertions(+), 11 deletions(-)
>>
>> diff --git a/tools/perf/util/bpf_counter.c b/tools/perf/util/bpf_counter.c
>> index 7a8af60e0f51..e07ff04b934f 100644
>> --- a/tools/perf/util/bpf_counter.c
>> +++ b/tools/perf/util/bpf_counter.c
>> @@ -529,9 +529,6 @@ 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 +540,7 @@ 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)
>> @@ -553,10 +551,11 @@ 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->init_filter_entries = filter_entry_cnt;
>
> Do you need this in the BPF program?
No need. Actually, this variable is only used in bperf__read().
Since bperf__read() does not have a `struct target` parameter, it is not possible to check the
filter_entry_cnt value again through bperf_check_target(). We can only put it in a global scope,
one way is the current implementation, and another way is to declare a global variable in bpf_counter.
Maybe the second way is more appropriate? If so, I will modify it.
>
>>
>> err = bperf_follower_bpf__attach(evsel->follower_skel);
>>
>> @@ -623,7 +622,7 @@ 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 < skel->bss->init_filter_entries; 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..59fab421526a 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;
>> +__u32 init_filter_entries = 0;
>>
>> 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();
>> @@ -55,16 +61,20 @@ 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 +85,57 @@ int BPF_PROG(fexit_XXX)
>> return 0;
>> }
>>
>> +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;
>> +
>> + if (type != BPERF_FILTER_PID && type != BPERF_FILTER_TGID)
>> + return 0;
>
> I think you can load/attach this program only if the type is either
> PID or TGID. Then it'd reduce the overhead.
Great suggestion, I'll give it a try.
>
>> +
>> + parent_pid = bpf_get_current_pid_tgid() >> 32;
>> + child_pid = task->pid;
>> +
>> + /* 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;
>> +}
>> +
>> +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;
>> +
>> + if (type != BPERF_FILTER_PID && type != BPERF_FILTER_TGID)
>> + return 0;
>
> Ditto.
>
> Thanks,
> Namhyung
>
>> +
>> + /* 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
>>
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