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Thu, 03 Sep 2026 00:21:20 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([195.174.135.130]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49cee60d9c6sm49952545e9.11.2026.09.03.00.21.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Sep 2026 00:21:20 -0700 (PDT) Message-ID: Subject: Re: [RFC PATCH 00/20] rv: Add support for BPF monitors From: Gabriele Monaco To: Alexei Starovoitov , Nam Cao , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org Cc: Steven Rostedt , Wen Yang , Tobias Schaffner , Viktor Malik Date: Thu, 03 Sep 2026 09:21:18 +0200 In-Reply-To: References: <20260831090524.106845-1-gmonaco@redhat.com> <87se3sakgi.fsf@yellow.woof> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0BrZXJuZWwub3JnPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmjKX2MCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfIQuAD+JulczTN6l7oJjyroySU55Fbjdvo52xiYYlMjPG7dCTsBAMFI7dSL5zg98I+8 cXY1J7kyNsY6/dcipqBM4RMaxXsOtCRHYWJyaWVsZSBNb25hY28gPGdtb25hY29AcmVkaGF0LmNvb T6InAQTFgoARAIbAwUJBaOagAULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgBYhBMrKEfgLgd0WcK eo9u9KbElYeE3yBQJoymCyAhkBAAoJEO9KbElYeE3yjX4BAJ/ETNnlHn8OjZPT77xGmal9kbT1bC1 7DfrYVISWV2Y1AP9HdAMhWNAvtCtN2S1beYjNybuK6IzWYcFfeOV+OBWRDQ== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2026-09-02 at 18:57 -0700, Alexei Starovoitov wrote: > I don't think bpf fits here. I haven't seen active use of RV and even les= s > so of any request from people who want this kind of programmability. >=20 > So Nack for now. Sorry. Thanks for your opinion, however it sounds a bit harsh to me. RV is clearly not a popular tool, but I wouldn't say it doesn't have active= use: we're actively using it to validate the deadline scheduler/server changes a= nd it already found a number of issues (e.g. [1], [2]). The RTapp monitors are used to validate if userspace real-time applications interact with the kernel in the best way for predictability, as far as I'm = aware that's regularly used [3]. In my eyes, the missing piece of RV is in fact this programmability. Adding= a monitor now requires to write in-tree built-in kernel code. There are strong use cases for domain-specific rules that aren't general en= ough to belong in the kernel tree: * stricter RTapp rules that may not apply to all use-cases * verify some exotic system within Linux (e.g. a co-kernel [4]) * modelling for functional safety certification process (used for in-vehicl= e OSes like RHIVOS) BPF seems the natural tool for the job to me. Mind that RV monitors would b= e simple users of BPF, requiring only modifications in the RV subsystem but u= sing standard BPF facilities. I'm totally open to discuss on this though. Thanks, Gabriele [1] - https://lore.kernel.org/lkml/20260522125833.264145-1-gmonaco@redhat.c= om [2] - https://lore.kernel.org/lkml/20260113085159.114226-3-gmonaco@redhat.c= om [3] - https://lore.kernel.org/linux-rt-users/20260826132153.2476006-1-bigeasy@lin= utronix.de/T/#t [4] - https://lore.kernel.org/lkml/20260827072400.45734-1-tobias.schaffner@siemen= s.com