From: Valentin Schneider <valentin.schneider@arm.com>
To: Benjamin GAIGNARD <benjamin.gaignard@st.com>
Cc: 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>,
"vincent.guittot\@linaro.org" <vincent.guittot@linaro.org>,
"rjw\@rjwysocki.net" <rjw@rjwysocki.net>
Subject: Re: [PATCH] media: stm32-dcmi: Set minimum cpufreq requirement
Date: Tue, 02 Jun 2020 14:35:31 +0100 [thread overview]
Message-ID: <jhjo8q1io9o.mognet@arm.com> (raw)
In-Reply-To: <f95ce45f-7a1c-0feb-afa8-203ddb500f2f@st.com>
On 02/06/20 12:37, Benjamin GAIGNARD wrote:
> On 6/2/20 11:31 AM, Valentin Schneider wrote:
>>> @@ -99,6 +100,8 @@ enum state {
>>>
>>> #define OVERRUN_ERROR_THRESHOLD 3
>>>
>>> +#define DCMI_MIN_FREQ 650000 /* in KHz */
>>> +
>> This assumes the handling part is guaranteed to always run on the same CPU
>> with the same performance profile (regardless of the platform). If that's
>> not guaranteed, it feels like you'd want this to be configurable in some
>> way.
> Yes I could add a st,stm32-dcmi-min-frequency (in KHz) parameter the
> device tree node.
>
Something like that - I'm not sure how well this fits with the DT
landscape, as you could argue it isn't really a description of the
hardware, more of a description of the performance expectations of the
software. I won't really argue here.
>>
>>> struct dcmi_graph_entity {
>>> struct v4l2_async_subdev asd;
>>>
>> [...]
>>> @@ -2020,6 +2042,8 @@ static int dcmi_probe(struct platform_device *pdev)
>>> goto err_cleanup;
>>> }
>>>
>>> + dcmi->policy = cpufreq_cpu_get(0);
>>> +
>> Ideally you'd want to fetch the policy of the CPU your IRQ (and handling
>> thread) is affined to; The only compatible DTS I found describes a single
>> A7, which is somewhat limited in the affinity area...
> If I move this code just before start streaming and use get_cpu(), would
> it works ?
>
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.
> Benjamin
>>
>>> dev_info(&pdev->dev, "Probe done\n");
>>>
>>> platform_set_drvdata(pdev, dcmi);
>>> @@ -2049,6 +2073,9 @@ static int dcmi_remove(struct platform_device *pdev)
>>>
>>> pm_runtime_disable(&pdev->dev);
>>>
>>> + if (dcmi->policy)
>>> + cpufreq_cpu_put(dcmi->policy);
>>> +
>>> v4l2_async_notifier_unregister(&dcmi->notifier);
>>> v4l2_async_notifier_cleanup(&dcmi->notifier);
>>> media_entity_cleanup(&dcmi->vdev->entity);
next prev parent reply other threads:[~2020-06-02 13:35 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-27 15:16 [PATCH] media: stm32-dcmi: Set minimum cpufreq requirement Benjamin Gaignard
2020-06-02 8:29 ` Hugues FRUCHET
2020-06-02 9:31 ` Valentin Schneider
2020-06-02 11:37 ` Benjamin GAIGNARD
2020-06-02 13:35 ` Valentin Schneider [this message]
2020-06-03 7:34 ` Benjamin GAIGNARD
2020-06-03 7:50 ` Vincent Guittot
2020-06-03 9:41 ` Valentin Schneider
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