linux-kernel - [RFC RESEND 0/3] Introduce cpufreq minimum load QoS

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Message-ID: <20200526151619.8779-1-benjamin.gaignard@st.com>
Date:   Tue, 26 May 2020 17:16:16 +0200
From:   Benjamin Gaignard <benjamin.gaignard@...com>
To:     <rjw@...ysocki.net>, <viresh.kumar@...aro.org>,
        <hugues.fruchet@...com>, <mchehab@...nel.org>,
        <mcoquelin.stm32@...il.com>, <alexandre.torgue@...com>,
        <pavel@....cz>, <len.brown@...el.com>,
        <valentin.schneider@....com>, <vincent.guittot@...aro.org>
CC:     <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-media@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        Benjamin Gaignard <benjamin.gaignard@...com>
Subject: [RFC RESEND 0/3] Introduce cpufreq minimum load QoS

A first round [1] of discussions and suggestions have already be done on 
this series but without found a solution to the problem. I resend it to
progress on this topic.

When start streaming from the sensor the CPU load could remain very low 
because almost all the capture pipeline is done in hardware (i.e. without 
using the CPU) and let believe to cpufreq governor that it could use lower 
frequencies. If the governor decides to use a too low frequency that 
becomes a problem when we need to acknowledge the interrupt during the 
blanking time.
The delay to ack the interrupt and perform all the other actions before
the next frame is very short and doesn't allow to the cpufreq governor to
provide the required burst of power. That led to drop the half of the frames.

To avoid this problem, DCMI driver informs the cpufreq governors by adding
a cpufreq minimum load QoS resquest.

Benjamin 

[1] https://lkml.org/lkml/2020/4/24/360

Benjamin Gaignard (3):
  PM: QoS: Introduce cpufreq minimum load QoS
  cpufreq: governor: Use minimum load QoS
  media: stm32-dcmi: Inform cpufreq governors about cpu load needs

 drivers/cpufreq/cpufreq_governor.c        |   5 +
 drivers/media/platform/stm32/stm32-dcmi.c |   8 ++
 include/linux/pm_qos.h                    |  12 ++
 kernel/power/qos.c                        | 213 ++++++++++++++++++++++++++++++
 4 files changed, 238 insertions(+)

-- 
2.15.0