Re: [PATCH] perflib: deprecate bpf_map__resize in favor of bpf_map_set_max_entries

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Muhammad Falak R Wani <falakreyaz@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Quentin Monnet <quentin@isovalent.com>,
	Yu Kuai <yukuai3@huawei.com>,
	"linux-perf-use." <linux-perf-users@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH] perflib: deprecate bpf_map__resize in favor of bpf_map_set_max_entries
Date: Mon, 16 Aug 2021 12:28:14 -0700	[thread overview]
Message-ID: <CAEf4BzZ+3hM9oPxdXsxXRKJD2TCmpXPnkWz1LPnP7mDagprdyA@mail.gmail.com> (raw)
In-Reply-To: <20210815103610.27887-1-falakreyaz@gmail.com>

On Sun, Aug 15, 2021 at 3:36 AM Muhammad Falak R Wani
<falakreyaz@gmail.com> wrote:
>
> As a part of libbpf 1.0 plan[0], this patch deprecates use of
> bpf_map__resize in favour of bpf_map__set_max_entries.
>
> Reference: https://github.com/libbpf/libbpf/issues/304
> [0]: https://github.com/libbpf/libbpf/wiki/Libbpf:-the-road-to-v1.0#libbpfh-high-level-apis
>
> Signed-off-by: Muhammad Falak R Wani <falakreyaz@gmail.com>
> ---

All looks good, there is an opportunity to simplify the code a bit (see below).

Arnaldo, I assume you'll take this through your tree or you'd like us
to take it through bpf-next?

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>  tools/perf/util/bpf_counter.c        | 8 ++++----
>  tools/perf/util/bpf_counter_cgroup.c | 8 ++++----
>  2 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/util/bpf_counter.c b/tools/perf/util/bpf_counter.c
> index ba0f20853651..ced2dac31dcf 100644
> --- a/tools/perf/util/bpf_counter.c
> +++ b/tools/perf/util/bpf_counter.c
> @@ -127,9 +127,9 @@ static int bpf_program_profiler_load_one(struct evsel *evsel, u32 prog_id)
>
>         skel->rodata->num_cpu = evsel__nr_cpus(evsel);
>
> -       bpf_map__resize(skel->maps.events, evsel__nr_cpus(evsel));
> -       bpf_map__resize(skel->maps.fentry_readings, 1);
> -       bpf_map__resize(skel->maps.accum_readings, 1);
> +       bpf_map__set_max_entries(skel->maps.events, evsel__nr_cpus(evsel));
> +       bpf_map__set_max_entries(skel->maps.fentry_readings, 1);
> +       bpf_map__set_max_entries(skel->maps.accum_readings, 1);
>
>         prog_name = bpf_target_prog_name(prog_fd);
>         if (!prog_name) {
> @@ -399,7 +399,7 @@ static int bperf_reload_leader_program(struct evsel *evsel, int attr_map_fd,
>                 return -1;
>         }
>
> -       bpf_map__resize(skel->maps.events, libbpf_num_possible_cpus());
> +       bpf_map__set_max_entries(skel->maps.events, libbpf_num_possible_cpus());

If you set max_entries to 0 (or just skip specifying it) for events
map in util/bpf_skel/bperf_cgroup.bpf.c, you won't need to resize it,
libbpf will automatically size it to number of possible CPUs.

>         err = bperf_leader_bpf__load(skel);
>         if (err) {
>                 pr_err("Failed to load leader skeleton\n");
> diff --git a/tools/perf/util/bpf_counter_cgroup.c b/tools/perf/util/bpf_counter_cgroup.c
> index 89aa5e71db1a..cbc6c2bca488 100644
> --- a/tools/perf/util/bpf_counter_cgroup.c
> +++ b/tools/perf/util/bpf_counter_cgroup.c
> @@ -65,14 +65,14 @@ static int bperf_load_program(struct evlist *evlist)
>
>         /* we need one copy of events per cpu for reading */
>         map_size = total_cpus * evlist->core.nr_entries / nr_cgroups;
> -       bpf_map__resize(skel->maps.events, map_size);
> -       bpf_map__resize(skel->maps.cgrp_idx, nr_cgroups);
> +       bpf_map__set_max_entries(skel->maps.events, map_size);
> +       bpf_map__set_max_entries(skel->maps.cgrp_idx, nr_cgroups);
>         /* previous result is saved in a per-cpu array */
>         map_size = evlist->core.nr_entries / nr_cgroups;
> -       bpf_map__resize(skel->maps.prev_readings, map_size);
> +       bpf_map__set_max_entries(skel->maps.prev_readings, map_size);
>         /* cgroup result needs all events (per-cpu) */
>         map_size = evlist->core.nr_entries;
> -       bpf_map__resize(skel->maps.cgrp_readings, map_size);
> +       bpf_map__set_max_entries(skel->maps.cgrp_readings, map_size);
>
>         set_max_rlimit();
>
> --
> 2.17.1
>