linux-kernel - Re: [PATCH v4] perf tools: Get a perf cgroup more portably in BPF

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Date:   Mon, 26 Sep 2022 14:06:46 +0100
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, Song Liu <songliubraving@...com>,
        Hao Luo <haoluo@...gle.com>, bpf@...r.kernel.org
Subject: Re: [PATCH v4] perf tools: Get a perf cgroup more portably in BPF

Em Thu, Sep 22, 2022 at 11:32:05PM -0700, Namhyung Kim escreveu:
> The perf_event_cgrp_id can be different on other configurations.
> To be more portable as CO-RE, it needs to get the cgroup subsys id
> using the bpf_core_enum_value() helper.
> 
> Suggested-by: Ian Rogers <irogers@...gle.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> v4 changes)
>  * add a missing check in the off_cpu

Thanks, applied.

- Arnaldo

 
> v3 changes)
>  * check compiler features for enum value
> 
> v2 changes)
>  * fix off_cpu.bpf.c too
>  * get perf_subsys_id only once
> 
>  tools/perf/util/bpf_skel/bperf_cgroup.bpf.c | 11 ++++++++++-
>  tools/perf/util/bpf_skel/off_cpu.bpf.c      | 18 ++++++++++++++----
>  2 files changed, 24 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c b/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c
> index 292c430768b5..8e7520e273db 100644
> --- a/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c
> +++ b/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c
> @@ -48,6 +48,7 @@ const volatile __u32 num_cpus = 1;
>  
>  int enabled = 0;
>  int use_cgroup_v2 = 0;
> +int perf_subsys_id = -1;
>  
>  static inline int get_cgroup_v1_idx(__u32 *cgrps, int size)
>  {
> @@ -58,7 +59,15 @@ static inline int get_cgroup_v1_idx(__u32 *cgrps, int size)
>  	int level;
>  	int cnt;
>  
> -	cgrp = BPF_CORE_READ(p, cgroups, subsys[perf_event_cgrp_id], cgroup);
> +	if (perf_subsys_id == -1) {
> +#if __has_builtin(__builtin_preserve_enum_value)
> +		perf_subsys_id = bpf_core_enum_value(enum cgroup_subsys_id,
> +						     perf_event_cgrp_id);
> +#else
> +		perf_subsys_id = perf_event_cgrp_id;
> +#endif
> +	}
> +	cgrp = BPF_CORE_READ(p, cgroups, subsys[perf_subsys_id], cgroup);
>  	level = BPF_CORE_READ(cgrp, level);
>  
>  	for (cnt = 0; i < MAX_LEVELS; i++) {
> diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
> index c4ba2bcf179f..38e3b287dbb2 100644
> --- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
> +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
> @@ -94,6 +94,8 @@ const volatile bool has_prev_state = false;
>  const volatile bool needs_cgroup = false;
>  const volatile bool uses_cgroup_v1 = false;
>  
> +int perf_subsys_id = -1;
> +
>  /*
>   * 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:
> @@ -119,11 +121,19 @@ static inline __u64 get_cgroup_id(struct task_struct *t)
>  {
>  	struct cgroup *cgrp;
>  
> -	if (uses_cgroup_v1)
> -		cgrp = BPF_CORE_READ(t, cgroups, subsys[perf_event_cgrp_id], cgroup);
> -	else
> -		cgrp = BPF_CORE_READ(t, cgroups, dfl_cgrp);
> +	if (!uses_cgroup_v1)
> +		return BPF_CORE_READ(t, cgroups, dfl_cgrp, kn, id);
> +
> +	if (perf_subsys_id == -1) {
> +#if __has_builtin(__builtin_preserve_enum_value)
> +		perf_subsys_id = bpf_core_enum_value(enum cgroup_subsys_id,
> +						     perf_event_cgrp_id);
> +#else
> +		perf_subsys_id = perf_event_cgrp_id;
> +#endif
> +	}
>  
> +	cgrp = BPF_CORE_READ(t, cgroups, subsys[perf_subsys_id], cgroup);
>  	return BPF_CORE_READ(cgrp, kn, id);
>  }
>  
> -- 
> 2.37.3.998.g577e59143f-goog

-- 

- Arnaldo