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Wed, 21 Oct 2026 01:46:14 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([195.174.34.203]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e2583ffa8sm4205103f8f.51.2026.10.21.01.46.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Oct 2026 01:46:13 -0700 (PDT) Message-ID: <631896ae8e44ed6356c3b79598a2facee8af9770.camel@redhat.com> Subject: Re: [PATCH v2 10/15] tools/rv: Add BPF monitors From: Gabriele Monaco To: Nam Cao , John Ogness , Alexei Starovoitov , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, Steven Rostedt Cc: Wen Yang , Tobias Schaffner , Viktor Malik Date: Wed, 21 Oct 2026 10:46:11 +0200 In-Reply-To: <87ecdjqxnr.fsf@yellow.woof> References: <20261001152042.124445-1-gmonaco@redhat.com> <20261001152042.124445-11-gmonaco@redhat.com> <878q3xtptq.fsf@jogness.linutronix.de> <8B3FF026-6159-48CF-8FEA-AF2FACD2E4EB@redhat.com> <87bj8s8ih9.fsf@jogness.linutronix.de> <871p9mqcn2.fsf@jogness.linutronix.de> <87ld7trgzg.fsf@yellow.woof> <87mrs9q1d3.fsf@jogness.linutronix.de> <87ecdjqxnr.fsf@yellow.woof> Autocrypt: addr=gmonaco@redhat.com; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2026-10-21 at 10:13 +0200, Nam Cao wrote: > John Ogness writes: > > On 2026-10-19, Nam Cao wrote: > > > John Ogness writes: > > > > @namcao: Maybe you could chime in if you want the transitions as ev= ents. > > >=20 > > > No. Those are only useful for debugging RV itself and do not need to = be > > > upstream. > >=20 > > Sure, but debugging RV itself _is_ a use case. Especially when RV moves > > to eBPF and lots of people will start writing their own RV monitors. >=20 > Right. >=20 > I wouldn't enable those by default though, it's way too much noises. As > it's for debugging the model, we can have some sort of compile-time > switch to turn it on. That's almost what's happening already, in-kernel use tracepoints, gated by static branches. Those are the closest thing you can get to a dynamic compi= le- time switch (assuming such a thing can exist), it's patching the code. BPF gets even closer to the concept, we use a volatile const flag, which is constant for the JIT runtime but volatile for the compiler (not compiled ou= t when generating byte code). Before loading we set the value we want in the object and the JIT compiler wipes away the unused branches. But technicalities aside, we probably want tracepoints for events too, so bpf_printk or whatever else. Gabriele