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Wed, 16 Jul 2025 06:40:16 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGmL4ysrFH4w0DELpct967Iu0YF4NtKCmmoy2wzP/5le1HZ4rifdgWb0k5u+DI9u9En6Wo/hg== X-Received: by 2002:a05:600c:4590:b0:442:c993:6f94 with SMTP id 5b1f17b1804b1-4562dfe7998mr35599565e9.12.1752673215500; Wed, 16 Jul 2025 06:40:15 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([185.107.56.42]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8e14e82sm18042152f8f.71.2025.07.16.06.40.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Jul 2025 06:40:15 -0700 (PDT) Message-ID: <122cfd4ba6b0805e91ff09526d5d159ff3871964.camel@redhat.com> 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 15:40:13 +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() ? >=20 > > @@ -6786,6 +6793,7 @@ static void __sched notrace __schedule(int > > sched_mode) > > =C2=A0 rq =3D context_switch(rq, prev, next, &rf); > > =C2=A0 } else { > > =C2=A0 rq_unpin_lock(rq, &rf); > > + trace_sched_switch_vain_tp(preempt, prev, > > prev_state); > > =C2=A0 __balance_callbacks(rq); > > =C2=A0 raw_spin_rq_unlock_irq(rq); > > =C2=A0 } >=20 > Hurmph... don't you already have this covered by: > trace_sched_exit_tp() ? >=20 > Specifically, the only case where is_switch :=3D false, is this case. Mostly, it may work in some cases, but sched_exit happens with interrupt enabled while all types of switches (including the vain ones) must occur with interrupt disabled. Some assumptions don't stand without this tracepoint, but I guess I could adapt monitors to live without this if you believe it's not worth adding a new tracepoint there. Thanks, Gabriele