linux-kernel - Re: [PATCH v8 04/10] perf record --off-cpu: Preparation of off-cpu BPF program

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Message-ID: <CAP-5=fXPCgXyp3w478M9UrqVmneg1mvsabSJb55R+-xPYaUFuw@mail.gmail.com>
Date: Wed, 13 Nov 2024 09:03:25 -0800
From: Ian Rogers <irogers@...gle.com>
To: Howard Chu <howardchu95@...il.com>
Cc: acme@...nel.org, peterz@...radead.org, namhyung@...nel.org, 
	mingo@...hat.com, jolsa@...nel.org, adrian.hunter@...el.com, 
	kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, James Clark <james.clark@...aro.org>, 
	Mark Rutland <mark.rutland@....com>, Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH v8 04/10] perf record --off-cpu: Preparation of off-cpu
 BPF program

On Tue, Nov 12, 2024 at 4:28 PM Howard Chu <howardchu95@...il.com> wrote:
>
> Set the perf_event map in BPF for dumping off-cpu samples.
>
> Set the offcpu_thresh to specify the threshold.
>
> Reviewed-by: Ian Rogers <irogers@...gle.com>
> Signed-off-by: Howard Chu <howardchu95@...il.com>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: James Clark <james.clark@...aro.org>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Kan Liang <kan.liang@...ux.intel.com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Link: https://lore.kernel.org/r/20241108204137.2444151-5-howardchu95@gmail.com
> [ Added some missing iteration variables to off_cpu_config() and fixed up
>   a manually edited patch hunk line boundary line ]
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
>  tools/perf/util/bpf_off_cpu.c          | 25 +++++++++++++++++++++++++
>  tools/perf/util/bpf_skel/off_cpu.bpf.c | 11 +++++++++++
>  2 files changed, 36 insertions(+)
>
> diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
> index 558c5e5c2dc3..61729a65b529 100644
> --- a/tools/perf/util/bpf_off_cpu.c
> +++ b/tools/perf/util/bpf_off_cpu.c
> @@ -13,6 +13,7 @@
>  #include "util/cgroup.h"
>  #include "util/strlist.h"
>  #include <bpf/bpf.h>
> +#include <internal/xyarray.h>
>
>  #include "bpf_skel/off_cpu.skel.h"
>
> @@ -60,6 +61,9 @@ static int off_cpu_config(struct evlist *evlist)
>  static void off_cpu_start(void *arg)
>  {
>         struct evlist *evlist = arg;
> +       struct evsel *evsel;
> +       struct perf_cpu pcpu;
> +       int i;
>
>         /* update task filter for the given workload */
>         if (skel->rodata->has_task && skel->rodata->uses_tgid &&
> @@ -73,6 +77,25 @@ static void off_cpu_start(void *arg)
>                 bpf_map_update_elem(fd, &pid, &val, BPF_ANY);
>         }
>
> +       /* update BPF perf_event map */
> +       evsel = evlist__find_evsel_by_str(evlist, OFFCPU_EVENT);
> +       if (evsel == NULL) {
> +               pr_err("%s evsel not found\n", OFFCPU_EVENT);
> +               return;
> +       }
> +
> +       perf_cpu_map__for_each_cpu(pcpu, i, evsel->core.cpus) {
> +               int err;
> +
> +               err = bpf_map__update_elem(skel->maps.offcpu_output, &pcpu.cpu, sizeof(__u32),
> +                                          xyarray__entry(evsel->core.fd, i, 0),
> +                                          sizeof(__u32), BPF_ANY);
> +               if (err) {
> +                       pr_err("Failed to update perf event map for direct off-cpu dumping\n");
> +                       return;
> +               }
> +       }
> +
>         skel->bss->enabled = 1;
>  }
>
> @@ -261,6 +284,8 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target,
>                 }
>         }
>
> +       skel->bss->offcpu_thresh_ns = opts->off_cpu_thresh_us * 1000;

Thanks for the suffixes, readability++.

Ian

> +
>         err = off_cpu_bpf__attach(skel);
>         if (err) {
>                 pr_err("Failed to attach off-cpu BPF skeleton\n");
> diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
> index c152116df72f..c87132e01eb3 100644
> --- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
> +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
> @@ -18,6 +18,8 @@
>  #define MAX_STACKS   32
>  #define MAX_ENTRIES  102400
>
> +#define MAX_CPUS  4096
> +
>  struct tstamp_data {
>         __u32 stack_id;
>         __u32 state;
> @@ -39,6 +41,13 @@ struct {
>         __uint(max_entries, MAX_ENTRIES);
>  } stacks SEC(".maps");
>
> +struct {
> +       __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
> +       __uint(key_size, sizeof(__u32));
> +       __uint(value_size, sizeof(__u32));
> +       __uint(max_entries, MAX_CPUS);
> +} offcpu_output SEC(".maps");
> +
>  struct {
>         __uint(type, BPF_MAP_TYPE_TASK_STORAGE);
>         __uint(map_flags, BPF_F_NO_PREALLOC);
> @@ -97,6 +106,8 @@ const volatile bool uses_cgroup_v1 = false;
>
>  int perf_subsys_id = -1;
>
> +__u64 offcpu_thresh_ns;
> +
>  /*
>   * Old kernel used to call it task_struct->state and now it's '__state'.
>   * Use BPF CO-RE "ignored suffix rule" to deal with it like below:
> --
> 2.43.0
>