From: Valentin Schneider <valentin.schneider@arm.com> To: Vincent Guittot <vincent.guittot@linaro.org> Cc: Benjamin GAIGNARD <benjamin.gaignard@st.com>, Hugues FRUCHET <hugues.fruchet@st.com>, "mchehab\@kernel.org" <mchehab@kernel.org>, "mcoquelin.stm32\@gmail.com" <mcoquelin.stm32@gmail.com>, Alexandre TORGUE <alexandre.torgue@st.com>, "linux-media\@vger.kernel.org" <linux-media@vger.kernel.org>, "linux-stm32\@st-md-mailman.stormreply.com" <linux-stm32@st-md-mailman.stormreply.com>, "linux-arm-kernel\@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>, "rjw\@rjwysocki.net" <rjw@rjwysocki.net> Subject: Re: [PATCH] media: stm32-dcmi: Set minimum cpufreq requirement Date: Wed, 03 Jun 2020 10:41:41 +0100 [thread overview] Message-ID: <jhjmu5kiizu.mognet@arm.com> (raw) In-Reply-To: <CAKfTPtCbM-w_0VrTB5tsSM5PKRtC44f3sSmAR=U=P3e3KQ+cMw@mail.gmail.com> On 03/06/20 08:50, Vincent Guittot wrote: > On Wed, 3 Jun 2020 at 09:34, Benjamin GAIGNARD <benjamin.gaignard@st.com> wrote: >> On 6/2/20 3:35 PM, Valentin Schneider wrote: >> > AFAIA streaming_start() is not necessarily executing on the same CPU as the >> > one that will handle the interrupt. I was thinking you could use the IRQ's >> > effective affinity as a hint of which CPU(s) to boost, i.e. something like: >> > >> > --- >> > struct cpumask_var_t visited; >> > struct irq_data *d = irq_get_irq_data(irq); >> > >> > err = alloc_cpumask_var(visited, GFP_KERNEL); >> > /* ... */ >> > for_each_cpu(cpu, irq_data_get_effective_affinity_mask(d)) { >> > /* check if not already spanned */ >> > if (cpumask_test_cpu(cpu, visited)) >> > continue; >> > >> > policy = cpufreq_cpu_get(cpu); >> > cpumask_or(visited, visited, policy->cpus); >> > /* do the boost for that policy here */ >> > /* ... */ >> > cpufreq_cpu_put(policy); >> > } >> > --- >> > >> > That of course falls apart when hotplug gets involved, and the effective >> > affinity changes... There's irq_set_affinity_notifier() out there, but it >> > seems it's only about the affinity, not the effective_affinity, I'm not >> > sure how valid it would be to query the effective_affinity in that >> > notifier. >> If I wait to be in the irq it will be too late so I think I will do a >> loop over all possible CPUs >> before start the streaming to change the policies. > Yes, that's what I was thinking as well. > Can't you use irq_get_affinity_mask and loop over it ? > In the end that's the only usable option, I think. I was looking at alternatives because on arm64 (and AFAICT that applies to arm too; see irq-gic.c::gic_set_affinity()) the affinity mask spans all CPUs by default, while the effective affinity mask spans only the CPU that will actually handle the IRQ (+ where its thread should run). That said, using the effective mask that way does feel like an implementation leak. Sadly I couldn't find any better way to minimize the number of boosted frequency domains. > Also You should better use freq_qos_add/remove_request during probe > and remove of the driver and use freq_qos_update_request in > dcmi_start/stop_streaming to set/unset your constraint. >
WARNING: multiple messages have this Message-ID (diff)
From: Valentin Schneider <valentin.schneider@arm.com> To: Vincent Guittot <vincent.guittot@linaro.org> Cc: Benjamin GAIGNARD <benjamin.gaignard@st.com>, "rjw@rjwysocki.net" <rjw@rjwysocki.net>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Alexandre TORGUE <alexandre.torgue@st.com>, "mcoquelin.stm32@gmail.com" <mcoquelin.stm32@gmail.com>, Hugues FRUCHET <hugues.fruchet@st.com>, "mchehab@kernel.org" <mchehab@kernel.org>, "linux-stm32@st-md-mailman.stormreply.com" <linux-stm32@st-md-mailman.stormreply.com>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, "linux-media@vger.kernel.org" <linux-media@vger.kernel.org> Subject: Re: [PATCH] media: stm32-dcmi: Set minimum cpufreq requirement Date: Wed, 03 Jun 2020 10:41:41 +0100 [thread overview] Message-ID: <jhjmu5kiizu.mognet@arm.com> (raw) In-Reply-To: <CAKfTPtCbM-w_0VrTB5tsSM5PKRtC44f3sSmAR=U=P3e3KQ+cMw@mail.gmail.com> On 03/06/20 08:50, Vincent Guittot wrote: > On Wed, 3 Jun 2020 at 09:34, Benjamin GAIGNARD <benjamin.gaignard@st.com> wrote: >> On 6/2/20 3:35 PM, Valentin Schneider wrote: >> > AFAIA streaming_start() is not necessarily executing on the same CPU as the >> > one that will handle the interrupt. I was thinking you could use the IRQ's >> > effective affinity as a hint of which CPU(s) to boost, i.e. something like: >> > >> > --- >> > struct cpumask_var_t visited; >> > struct irq_data *d = irq_get_irq_data(irq); >> > >> > err = alloc_cpumask_var(visited, GFP_KERNEL); >> > /* ... */ >> > for_each_cpu(cpu, irq_data_get_effective_affinity_mask(d)) { >> > /* check if not already spanned */ >> > if (cpumask_test_cpu(cpu, visited)) >> > continue; >> > >> > policy = cpufreq_cpu_get(cpu); >> > cpumask_or(visited, visited, policy->cpus); >> > /* do the boost for that policy here */ >> > /* ... */ >> > cpufreq_cpu_put(policy); >> > } >> > --- >> > >> > That of course falls apart when hotplug gets involved, and the effective >> > affinity changes... There's irq_set_affinity_notifier() out there, but it >> > seems it's only about the affinity, not the effective_affinity, I'm not >> > sure how valid it would be to query the effective_affinity in that >> > notifier. >> If I wait to be in the irq it will be too late so I think I will do a >> loop over all possible CPUs >> before start the streaming to change the policies. > Yes, that's what I was thinking as well. > Can't you use irq_get_affinity_mask and loop over it ? > In the end that's the only usable option, I think. I was looking at alternatives because on arm64 (and AFAICT that applies to arm too; see irq-gic.c::gic_set_affinity()) the affinity mask spans all CPUs by default, while the effective affinity mask spans only the CPU that will actually handle the IRQ (+ where its thread should run). That said, using the effective mask that way does feel like an implementation leak. Sadly I couldn't find any better way to minimize the number of boosted frequency domains. > Also You should better use freq_qos_add/remove_request during probe > and remove of the driver and use freq_qos_update_request in > dcmi_start/stop_streaming to set/unset your constraint. > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-06-03 9:41 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-05-27 15:16 [PATCH] media: stm32-dcmi: Set minimum cpufreq requirement Benjamin Gaignard 2020-05-27 15:16 ` Benjamin Gaignard 2020-06-02 8:29 ` Hugues FRUCHET 2020-06-02 8:29 ` Hugues FRUCHET 2020-06-02 9:31 ` Valentin Schneider 2020-06-02 9:31 ` Valentin Schneider 2020-06-02 11:37 ` Benjamin GAIGNARD 2020-06-02 11:37 ` Benjamin GAIGNARD 2020-06-02 13:35 ` Valentin Schneider 2020-06-02 13:35 ` Valentin Schneider 2020-06-03 7:34 ` Benjamin GAIGNARD 2020-06-03 7:34 ` Benjamin GAIGNARD 2020-06-03 7:50 ` Vincent Guittot 2020-06-03 7:50 ` Vincent Guittot 2020-06-03 9:41 ` Valentin Schneider [this message] 2020-06-03 9:41 ` Valentin Schneider
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