Re: [PATCH] perf record: Add doc for bpf event selection

From: Changbin Du
Date: Fri Feb 01 2019 - 08:45:02 EST


Sure, please check them in v2. Thanks!

On Fri, Feb 01, 2019 at 09:10:50AM +0100, Arnaldo Carvalho de Melo wrote:
> Em Fri, Feb 01, 2019 at 03:06:41AM +0000, Changbin Du escreveu:
> > Add document for how to pass bpf program with perf.
>
> That is a good start, see some comments below.
>
> > Signed-off-by: Changbin Du <changbin.du@xxxxxxxxx>
> > ---
> > tools/perf/Documentation/perf-record.txt | 13 +++++++++++++
> > 1 file changed, 13 insertions(+)
> >
> > diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
> > index d232b13ea713..0925d987cad0 100644
> > --- a/tools/perf/Documentation/perf-record.txt
> > +++ b/tools/perf/Documentation/perf-record.txt
> > @@ -88,6 +88,19 @@ OPTIONS
> > If you want to profile write accesses in [0x1000~1008), just set
> > 'mem:0x1000/8:w'.
> >
> > + - a bpf source file or object file to select events by a bpf program.
>
> A source file (ending in .c) or a precompiled object file (ending in .o)
> selects one or more BPF events.
>
> > + The bpf program can attach to variant perf events based on section
> The BPFa various
> > + names.
> > +
> > + When passing '.c', perf searches installed LLVM to compile it into
> a
> > + object file first. Optional clang options can be pased by option
> an
> > + '--clang-opt'.
> > +
> > + perf record --clang-opt "-DLINUX_VERSION_CODE=0x50000" \
> > + -e ./tests/bpf-script-example.c
> > +
> > + Note: '--clang-opt' must place before '--event'.
>
> Please mention ~/.perfconfig, that needs a section in the
> tools/perf/Documentation/perf-config.txt, for instance I have right now:
>
> [root@quaco ~]# cat ~/.perfconfig
> [llvm]
> dump-obj = true
> clang-opt = -g
>
> The 'clang-opt' is the same as the command line arg you documented
> above, dump object may be used to update a .o file, like:
>
> [root@quaco ~]# vim /home/acme/git/perf/tools/perf/examples/bpf/augmented_raw_syscalls.c
>
> # Do some changes, save
>
> [root@quaco ~]# perf record -e /home/acme/git/perf/tools/perf/examples/bpf/augmented_raw_syscalls.c sleep 1
> LLVM: dumping /home/acme/git/perf/tools/perf/examples/bpf/augmented_raw_syscalls.o
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.023 MB perf.data ]
> [root@quaco ~]#
>
> And if you are up to documenting the remaining features, which I'd
> encourage you, please take a look at:
>
> tools/perf/util/llvm-utils.c
>
> In the perf_llvm_config function. there are more things that needs
> documenting, and doing a:
>
> git blame tools/perf/util/llvm-utils.c
>
> Helps in getting the needed explanations, for instance, the original
> patch adding the .perfconfig section was this:
>
> git show aa61fd05ca796
>
> And it has, for instance, among others:
>
> # kbuild directory. If not set, use /lib/modules/`uname -r`/build.
> # If set to "" deliberately, skip kernel header auto-detector.
> kbuild-dir = "/path/to/kernel/build"
>
> # Options passed to 'make' when detecting kernel header options.
> kbuild-opts = "ARCH=x86_64"
>
> Thanks for working on documenting these features!
>
> - Arnaldo
>
>
> > +
> > - a group of events surrounded by a pair of brace ("{event1,event2,...}").
> > Each event is separated by commas and the group should be quoted to
> > prevent the shell interpretation. You also need to use --group on
> > --
> > 2.17.1
>
> --
>
> - Arnaldo

--
Cheers,
Changbin Du