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Message-ID: <ZtktBbcjSdVt4WtJ@google.com>
Date: Wed, 4 Sep 2024 21:01:09 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Tengda Wu <wutengda@...weicloud.com>
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
Subject: Re: [PATCH -next 1/2] perf stat: Support inherit events during
 fork() for bperf

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?

>  
>  	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.

> +
> +	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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