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From 6c509a3d144d46a11454d32d128d16e16602b50f Mon Sep 17 00:00:00 2001
From: Hans de Goede <hdegoede@redhat.com>
Date: Mon, 11 Mar 2024 15:15:20 +0100
Subject: [PATCH 17/21] libcamera: Add "Software ISP benchmarking"
documentation
Add a "Software ISP benchmarking" documentation section which describes
the performance/power consumption measurements used during
the Software ISP's development.
Reviewed-by: Milan Zamazal <mzamazal@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Stefan Klug <stefan.klug@ideasonboard.com>
---
Documentation/index.rst | 1 +
Documentation/meson.build | 1 +
Documentation/software-isp-benchmarking.rst | 82 +++++++++++++++++++++
3 files changed, 84 insertions(+)
create mode 100644 Documentation/software-isp-benchmarking.rst
diff --git a/Documentation/index.rst b/Documentation/index.rst
index 63fac72d..5442ae75 100644
--- a/Documentation/index.rst
+++ b/Documentation/index.rst
@@ -24,3 +24,4 @@
Lens driver requirements <lens_driver_requirements>
Python Bindings <python-bindings>
Camera Sensor Model <camera-sensor-model>
+ SoftwareISP Benchmarking <software-isp-benchmarking>
diff --git a/Documentation/meson.build b/Documentation/meson.build
index 7a58fec8..3872e0a8 100644
--- a/Documentation/meson.build
+++ b/Documentation/meson.build
@@ -80,6 +80,7 @@ if sphinx.found()
'lens_driver_requirements.rst',
'python-bindings.rst',
'sensor_driver_requirements.rst',
+ 'software-isp-benchmarking.rst',
'../README.rst',
]
diff --git a/Documentation/software-isp-benchmarking.rst b/Documentation/software-isp-benchmarking.rst
new file mode 100644
index 00000000..b2803953
--- /dev/null
+++ b/Documentation/software-isp-benchmarking.rst
@@ -0,0 +1,82 @@
+.. SPDX-License-Identifier: CC-BY-SA-4.0
+
+.. _software-isp-benchmarking:
+
+Software ISP benchmarking
+=========================
+
+The Software ISP is particularly sensitive to performance regressions
+therefore it is a good idea to always benchmark the Software ISP
+before and after making changes to it and ensure that there are
+no performance regressions.
+
+DebayerCpu class builtin benchmark
+----------------------------------
+
+The DebayerCpu class has a builtin benchmark. This benchmark
+measures the time spent on processing (collecting statistics
+and debayering) only, it does not measure the time spent on
+capturing or outputting the frames.
+
+The builtin benchmark always runs. So this can be used by simply
+running "cam" or "qcam" with a pipeline using the Software ISP.
+
+When it runs it will skip measuring the first 30 frames to
+allow the caches and the CPU temperature (turbo-ing) to warm-up
+and then it measures 30 fps and shows the total and per frame
+processing time using an info level log message:
+
+.. code-block:: text
+
+ INFO Debayer debayer_cpu.cpp:907 Processed 30 frames in 244317us, 8143 us/frame
+
+To get stable measurements it is advised to disable any other processes which
+may cause significant CPU usage (e.g. disable wifi, bluetooth and browsers).
+When possible it is also advisable to disable CPU turbo-ing and
+frequency-scaling.
+
+For example when benchmarking on a Lenovo ThinkPad X1 Yoga Gen 8, with
+the charger plugged in, the CPU can be fixed to run at 2 GHz using:
+
+.. code-block:: shell
+
+ sudo x86_energy_perf_policy --turbo-enable 0
+ sudo cpupower frequency-set -d 2GHz -u 2GHz
+
+with these settings the builtin bench reports a processing time of ~7.8ms/frame
+on this laptop for FHD SGRBG10 (unpacked) bayer data.
+
+Measuring power consumption
+---------------------------
+
+Since the Software ISP is often used on mobile devices it is also
+important to measure power consumption and ensure that that does
+not regress.
+
+For example to measure power consumption on a Lenovo ThinkPad X1 Yoga Gen 8
+it needs to be running on battery and it should be configured with its
+platform-profile (/sys/firmware/acpi/platform_profile) set to balanced and
+with its default turbo and frequency-scaling behavior to match real world usage.
+
+Then start qcam to capture a FHD picture at 30 fps and position the qcam window
+so that it is fully visible. After this run the following command to monitor
+the power consumption:
+
+.. code-block:: shell
+
+ watch -n 10 cat /sys/class/power_supply/BAT0/power_now /sys/class/hwmon/hwmon6/fan?_input
+
+Note this not only measures the power consumption in µW it also monitors
+the speed of this laptop's 2 fans. This is important because depending on
+the ambient temperature the 2 fans may spin up while testing and this
+will cause an additional power consumption of approx. 0.5 W messing up
+the measurement.
+
+After starting qcam + the watch command let the laptop sit without using
+it for 2 minutes for the readings to stabilize. Then check that the fans
+have not turned on and manually take a couple of consecutive power readings
+and avarage these.
+
+On the example Lenovo ThinkPad X1 Yoga Gen 8 laptop this results in
+a measured power consumption of approx. 13 W while running qcam versus
+approx. 4-5 W while setting idle with its OLED panel on.
--
2.43.2
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