linux-kernel - Re: [PATCH v2 0/3] Use BPF filters for a "perf top -u" workaround

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Message-ID: <CAP-5=fU7V9F2vq=E=vHyD2E=ijx61UCsE=oywd3mTG7mnO3ttA@mail.gmail.com>
Date: Fri, 24 May 2024 13:22:43 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	Changbin Du <changbin.du@...wei.com>, John Fastabend <john.fastabend@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v2 0/3] Use BPF filters for a "perf top -u" workaround

On Fri, May 24, 2024 at 10:58 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Wed, May 22, 2024 at 09:38:57PM -0700, Namhyung Kim wrote:
> > On Mon, May 20, 2024 at 6:04 PM Ian Rogers <irogers@...gle.com> wrote:
> > >
> > > Allow uid and gid to be terms in BPF filters by first breaking the
> > > connection between filter terms and PERF_SAMPLE_xx values. Calculate
> > > the uid and gid using the bpf_get_current_uid_gid helper, rather than
> > > from a value in the sample. Allow filters to be passed to perf top, this allows:
> > >
> > > $ perf top -e cycles:P --filter "uid == $(id -u)"
> > >
> > > to work as a "perf top -u" workaround, as "perf top -u" usually fails
> > > due to processes/threads terminating between the /proc scan and the
> > > perf_event_open.
> > >
> > > v2. Allow PERF_SAMPLE_xx to be computed from the PBF_TERM_xx value
> > >     using a shift as requested by Namhyung.
> > >
> > > Ian Rogers (3):
> > >   perf bpf filter: Give terms their own enum
> > >   perf bpf filter: Add uid and gid terms
> > >   perf top: Allow filters on events
>
> Hmm.. I'm seeing this.
>
>   $ make build-test
>   ...
>   cd . && make GEN_VMLINUX_H=1 FEATURES_DUMP=/home/namhyung/project/linux/tools/perf/BUILD_TEST_FEATURE_DUMP -j64 O=/tmp/tmp.EeXFOfLPt5 DESTDIR=/tmp/tmp.Y0eiZKvc9D
>   ...
>     CLANG   /tmp/tmp.EeXFOfLPt5/util/bpf_skel/.tmp/sample_filter.bpf.o
>   In file included from util/bpf_skel/sample_filter.bpf.c:8:
>   In file included from util/bpf_skel/sample-filter.h:4:
>   /home/namhyung/project/linux/tools/include/uapi/linux/perf_event.h:29:6: error: redefinition of 'perf_type_id'
>   enum perf_type_id {
>        ^
>   /tmp/tmp.EeXFOfLPt5/util/bpf_skel/.tmp/../vmlinux.h:54086:6: note: previous definition is here
>   enum perf_type_id {
>        ^
>   In file included from util/bpf_skel/sample_filter.bpf.c:8:
>   In file included from util/bpf_skel/sample-filter.h:4:
>   /home/namhyung/project/linux/tools/include/uapi/linux/perf_event.h:30:2: error: redefinition of enumerator 'PERF_TYPE_HARDWARE'
>           PERF_TYPE_HARDWARE                      = 0,
>           ^
>   /tmp/tmp.EeXFOfLPt5/util/bpf_skel/.tmp/../vmlinux.h:54087:2: note: previous definition is here
>           PERF_TYPE_HARDWARE = 0,
>           ^
>   ...
>   make[3]: *** [Makefile.perf:264: sub-make] Error 2
>   make[2]: *** [Makefile:70: all] Error 2
>   make[1]: *** [tests/make:340: make_gen_vmlinux_h_O] Error 1
>   make: *** [Makefile:103: build-test] Error 2

IIRC this only exists for the sake of asserts. I can move the asserts
to placate the generated vmlinux.h. I'll send a v3.

Thanks,
Ian

> Thanks,
> Namhyung
>