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Thu, 24 Sep 2026 00:21:15 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([195.174.135.130]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-488684863fbsm11337269f8f.11.2026.09.24.00.21.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 00:21:15 -0700 (PDT) Message-ID: Subject: Re: [PATCH v2 1/3] rv: add per-edge dwell-time statistics primitive 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 09:21:13 +0200 In-Reply-To: <20260911123439.463052-2-tobias.schaffner@siemens.com> References: <20260911123439.463052-1-tobias.schaffner@siemens.com> <20260911123439.463052-2-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: > Add a small primitive that records, per automaton edge, how long the > monitor dwelled before taking it with a count, a sum and a maximum. >=20 > The counters are per-CPU and lock-free, so a monitor's hot path can > update them without disabling interrupts and without perturbing the laten= cy > being measured. Keep the state and its entry timestamp in one word so > nested transitions cannot charge a dwell to the wrong edge. >=20 > Signed-off-by: Tobias Schaffner > --- > =C2=A0include/rv/edge_stat.h | 69 +++++++++++++++++++++++++++++++++++++++= +++ > =C2=A01 file changed, 69 insertions(+) > =C2=A0create mode 100644 include/rv/edge_stat.h >=20 > diff --git a/include/rv/edge_stat.h b/include/rv/edge_stat.h ... > +#define RV_STATE_BITS 8 > +#define RV_STATE_MASK GENMASK(RV_STATE_BITS - 1, 0) > +#define RV_TS_MASK GENMASK(BITS_PER_LONG - RV_STATE_BITS - 1, 0) > + > +#define da_state_of(w) ((unsigned int)((w) & RV_STATE_MASK)) > +#define da_ts_of(w) ((u64)(w) >> RV_STATE_BITS) > +#define da_state_pack(s, ts) (((((da_state_t)(ts)) & RV_TS_MASK) << > RV_STATE_BITS) | \ > + ((da_state_t)(s) & RV_STATE_MASK)) These are barely readable and error prone, can you use FIELD_GET()/FIELD_PR= EP()? Thanks, Gabriele > + > +static __always_inline > +void rv_edge_stat_account(struct rv_edge_stat *s, u64 dwell_ns) > +{ > + s64 max; > + int i; > + > + local64_inc(&s->count); > + local64_add(dwell_ns, &s->sum_ns); > + > + /* Keep the largest dwell; bound retries if a nested update races us. > */ > + max =3D local64_read(&s->max_ns); > + for (i =3D 0; dwell_ns > (u64)max; i++) { > + if (i =3D=3D MAX_DA_RETRY_RACING_EVENTS) { > + WARN_ONCE(1, "rv: edge-stat max update exceeded %d > retries\n", > + =C2=A0 MAX_DA_RETRY_RACING_EVENTS); > + break; > + } > + if (local64_try_cmpxchg(&s->max_ns, &max, dwell_ns)) > + break; > + } > +} > + > +#endif /* CONFIG_RV_EDGE_STAT */ > + > +#endif /* _RV_EDGE_STAT_H */