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Wed, 02 Sep 2026 18:57:04 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 02 Sep 2026 18:57:03 -0700 Message-Id: Cc: "Steven Rostedt" , "Wen Yang" , "Tobias Schaffner" , "Viktor Malik" Subject: Re: [RFC PATCH 00/20] rv: Add support for BPF monitors From: "Alexei Starovoitov" To: "Gabriele Monaco" , "Nam Cao" , , , X-Mailer: aerc References: <20260831090524.106845-1-gmonaco@redhat.com> <87se3sakgi.fsf@yellow.woof> In-Reply-To: On Tue Sep 1, 2026 at 11:52 PM PDT, Gabriele Monaco wrote: > On Tue, 2026-09-01 at 20:35 +0200, Nam Cao wrote: >> Gabriele Monaco writes: >> > Extend the rv userspace tool to load BPF monitors, those can be found = in >> > specific locations (e.g. /usr/share/rv/bpf_monitors/) and are plain >> > object files including BTF data. >> >=20 >> > This type of BPF monitors can be generated from rvgen using the -b fla= g >> > just like in-kernel monitors and, after manual adaptation, can be buil= t >> > and run transparently by the rv userspace tool. >>=20 >> I am not familiar with BPF. What is the benefit of BPF monitors, >> compared to the existing DA monitors? > > I should definitely have included it in the cover letter.. I'm writing it > everywhere (will present at LPC) but forgot it here. > > Essentially BPF monitors can be pluggable, folks writing their own monito= rs > won't need to submit a patch or maintain a separate tree, which is useful= for > domain-specific models. > By being pluggable you also don't need to reboot to use a new/updated mon= itor. > > Think of being able to distribute a more granular set of rules for RTapp,= I > remember we had conversation along those lines, not all rules apply to al= l > contexts and what you send upstream has to be general, what you keep for > yourself doesn't. > > Having monitors in BPF brings also other perks over kernel modules: a who= le > bunch of readily available probe types (uprobes, fprobes, all unexported > tracepoints that are cumbersome for modules), the map infrastructure for > allocation is arguably easier and the code is verified when loaded agains= t > common issues (NULL pointer access, unbound loops, etc.). > > That said, I try to mimic as much as possible the in-kernel functionality= , but > some things are not the same (event/error tracepoints). > > These support DA only because BPF loading needs a userspace component and= the RV > tool doesn't support LTL and HA yet, there shouldn't be any technical rea= son not > to extend to those in the future. I don't think bpf fits here. I haven't seen active use of RV and even less so of any request from people who want this kind of programmability. So Nack for now. Sorry.