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Wed, 16 Jul 2025 08:09:46 -0700 (PDT) X-Google-Smtp-Source: AGHT+IF8tq87kRXSdlB+5Kbof387zmqH3pRO5qbk4swo5Gnn+EKJzZUxNtFjV0EHj+7pRXCTD5Wz/A== X-Received: by 2002:a5d:5f4e:0:b0:3b5:e6c0:1678 with SMTP id ffacd0b85a97d-3b60e52451dmr2476719f8f.45.1752678585835; Wed, 16 Jul 2025 08:09:45 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([185.107.56.42]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8dc2147sm18242526f8f.32.2025.07.16.08.09.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Jul 2025 08:09:45 -0700 (PDT) Message-ID: Subject: Re: [PATCH v3 12/17] sched: Adapt sched tracepoints for RV task model From: Gabriele Monaco To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Steven Rostedt , Masami Hiramatsu , linux-trace-kernel@vger.kernel.org, Nam Cao , Tomas Glozar , Juri Lelli , Clark Williams , John Kacur Date: Wed, 16 Jul 2025 17:09:43 +0200 In-Reply-To: <20250716123832.GW1613200@noisy.programming.kicks-ass.net> References: <20250715071434.22508-1-gmonaco@redhat.com> <20250715071434.22508-13-gmonaco@redhat.com> <20250716123832.GW1613200@noisy.programming.kicks-ass.net> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0ByZWRoYXQuY29tPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmbiuWMCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfJzZgD/TXjnqCyqaZH/Y2w+YVbvm93WX2eqBqiVZ6VEjTuGNs8A/iPrKbzdWC7AicnK xyhmqeUWOzFx5P43S1E1dhsrLWgP Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-1.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2025-07-16 at 14:38 +0200, Peter Zijlstra wrote: > On Tue, Jul 15, 2025 at 09:14:29AM +0200, Gabriele Monaco wrote: > > Add the following tracepoints: > > * sched_set_need_resched(tsk, cpu, tif) > > =C2=A0=C2=A0=C2=A0 Called when a task is set the need resched [lazy] fl= ag > > * sched_switch_vain(preempt, tsk, tsk_state) > > =C2=A0=C2=A0=C2=A0 Called when a task is selected again during __schedu= le > > =C2=A0=C2=A0=C2=A0 i.e. prev =3D=3D next =3D=3D tsk : no real context s= witch >=20 > > @@ -6592,6 +6598,7 @@ static bool try_to_block_task(struct rq *rq, > > struct task_struct *p, > > =C2=A0 int flags =3D DEQUEUE_NOCLOCK; > > =C2=A0 > > =C2=A0 if (signal_pending_state(task_state, p)) { > > + trace_sched_set_state_tp(p, TASK_RUNNING, true); > > =C2=A0 WRITE_ONCE(p->__state, TASK_RUNNING); > > =C2=A0 *task_state_p =3D TASK_RUNNING; > > =C2=A0 return false; >=20 > I'm confused on the purpose of this. How does this relate to say the > wakeup in signal_wake_up_state() ? Also this adds more context: models like sssw (in this series) expect that, after a task is set to sleepable, it either goes to sleep or is woken up/set to runnable. In this specific case, the task is set to runnable without tracing it, so the model doesn't know what happened, since it may not see a wakeup after that (the task is already runnable). Now I'm not sure if there are other events that we are guaranteed to see to reconstruct this specific case (at some point we should see the signal, I assume). This just simplified things as that is the only state change that was not traced. Am I missing anything obvious here? Thanks, Gabriele