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Thu, 24 Sep 2026 00:18:26 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([195.174.135.130]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-488684862a3sm11499823f8f.7.2026.09.24.00.18.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 00:18:26 -0700 (PDT) Message-ID: Subject: Re: [PATCH v2 3/3] rv: collect per-edge dwell time for per-cpu DA/HA monitors From: Gabriele Monaco To: Tobias Schaffner , Steven Rostedt Cc: Jonathan Corbet , Shuah Khan , Masami Hiramatsu , Mathieu Desnoyers , linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, rpm@xenomai.org, jan.kiszka@siemens.com Date: Thu, 24 Sep 2026 09:18:24 +0200 In-Reply-To: <20260911123439.463052-4-tobias.schaffner@siemens.com> References: <20260911123439.463052-1-tobias.schaffner@siemens.com> <20260911123439.463052-4-tobias.schaffner@siemens.com> 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-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2026-09-11 at 14:34 +0200, Tobias Schaffner wrote: > With the core facility in place, hook it into the DA/HA layer so that any > per-CPU automaton monitor also reports how long it lingers in each state. >=20 > Pack the automaton state and its entry timestamp into one word so the > transition cmpxchg updates both atomically. This prevents nested events > from attributing dwell time to the wrong edge and requires a native > 64-bit cmpxchg. >=20 > Account a transition as soon as its state change is committed. An HA > constraint that rejects the transition can therefore reset the monitor > without leaving an accounting window for nested events. >=20 > Add a selftest that enables a per-CPU monitor, checks the stats file > appears and is populated under load, and skips cleanly otherwise. >=20 > Signed-off-by: Tobias Schaffner > --- Sorry for taking that long, I could just have a quick look at your patches,= the approach looks fine but I'm going to need more time to check them carefully= , likely after the LPC conference. I'm not too fond of how you split into patches. What's the reason for split= ting 1/3 and 2/3 ? It seems they both add the new functionality, one step at a t= ime. ... > +/* Edge statistics pack the state and its entry timestamp into one word.= */ > +#ifdef CONFIG_RV_EDGE_STAT > +#define da_state_t unsigned long > +#else > +#define da_state_t unsigned int > +#endif Also try to define things in order, da_state_t is used in 2/3 but not defin= ed until 3/3. This doesn't break builds (the header is unused until 3/3) but i= s just harder to review. I find it more natural to split it into 1 add new functionality, 2 wire it,= 3 test it. What do you think? Thanks, Gabriele