linux-kernel - Re: [PATCH 4/5] perf ftrace: Add -b/--use-bpf option for latency subcommand

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAM9d7cgnQOZVaCs7Yj=siBLkhK7Z5TmmXLBA+VkGs1S3PUOSTw@mail.gmail.com>
Date:   Wed, 15 Dec 2021 10:15:48 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Song Liu <songliubraving@...com>,
        Changbin Du <changbin.du@...il.com>
Subject: Re: [PATCH 4/5] perf ftrace: Add -b/--use-bpf option for latency subcommand

On Mon, Dec 6, 2021 at 9:16 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Hello Athira,
>
> On Sun, Dec 5, 2021 at 6:24 PM Athira Rajeev
> <atrajeev@...ux.vnet.ibm.com> wrote:
> >
> >
> >
> > > On 30-Nov-2021, at 4:48 AM, Namhyung Kim <namhyung@...nel.org> wrote:
> > >
> > > The -b/--use-bpf option is to use BPF to get latency info of kernel
> > > functions.  It'd have better performance impact and I observed that
> > > latency of same function is smaller than before when using BPF.
> > >
> > > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > > ---
> [SNIP]
> > > @@ -1144,6 +1166,8 @@ int cmd_ftrace(int argc, const char **argv)
> > >       const struct option latency_options[] = {
> > >       OPT_CALLBACK('T', "trace-funcs", &ftrace.filters, "func",
> > >                    "Show latency of given function", parse_filter_func),
> > > +     OPT_BOOLEAN('b', "use-bpf", &ftrace.target.use_bpf,
> > > +                 "Use BPF to measure function latency"),
> >
> >
> > Hi Namhyung,
> >
> > Can this be inside BPF_SKEL check, similar to how we have “bpf-prog” and other options in builtin-stat.c ?
> >
> > #ifdef HAVE_BPF_SKEL
> > <<OPT_BOOLEAN for use-bpf>>
> > #endif
> >
> > Otherwise when using “-b” and if perf is not built with BPF_SKEL, we will just return in perf_ftrace__latency_prepare_bpf without any error messages.
>
> Thanks for reporting this.  Yeah, it should report
> error messages in such conditions.
>
> I think it'd be better to add an error message
> rather than hiding the option.

Well, now we build perf with BPF by default.
So I think it's ok to follow your suggestion.
it'd show the usage and options when the -b option is used
and BPF support is not enabled.

Thanks,
Namhyung