On 3/4/21 4:53 PM, Daniel Lezcano wrote:
Hi Lukasz,
thanks for commenting this patch,
On 04/03/2021 14:47, Lukasz Luba wrote:
Hi Daniel,
On 3/4/21 12:50 PM, Daniel Lezcano wrote:
Currently the default behavior is to manually having the devfreq
backend to register themselves as a devfreq cooling device.
There are no so many and actually it makes more sense to register the
devfreq device when adding it.
Consequently, every devfreq becomes a cooling device like cpufreq is.
Having a devfreq being registered as a cooling device can not mitigate
a thermal zone if it is not bound to this one. Thus, the current
configurations are not impacted by this change.
There are also different type of devices, which register into devfreq
framework like NoC buses, UFS/eMMC, jpeg and video accelerators, ISP,
etc.
In some platforms there are plenty of those devices and they all would
occupy memory due to private freq_table in devfreq_cooling, function:
devfreq_cooling_gen_tables().
IIRC in OdroidXU4 there are ~20 devfreq devs for NoC buses.
I'm curious, do you have a pointer to such kernels having all those
devfreq ?
Sure, it's mainline code, you can build it with exynos_defconfig.
You can check the DT files to find them arch/arm/boot/dts/exynos*.
(this particular OdroidXU4 is Exynos5422, but it grabs some generic dt
files).
Here is the mainline kernel content of /sys/class/devfreq/
----------------------------------------------------------
sys/class/devfreq /
10c20000.memory-controller soc:bus-g2d soc:bus-mfc
11800000.gpu soc:bus-g2d-acp soc:bus-mscl
soc:bus-disp1 soc:bus-gen soc:bus-noc
soc:bus-disp1-fimd soc:bus-gscl-scaler soc:bus-peri
soc:bus-fsys-apb soc:bus-jpeg soc:bus-wcore
soc:bus-fsys2 soc:bus-jpeg-apb
----------------------------------------------------------
IIRC some Odroid kernel maintained by Hardkernel had more devices
in this dir.
Here is how these bus devices print themselves during boot:
----------------------------------------------------------
[ 8.674840] exynos-bus: new bus device registered: soc:bus-wcore (
88700 KHz ~ 532000 KHz)
[ 8.686412] exynos-bus: new bus device registered: soc:bus-noc (
66600 KHz ~ 111000 KHz)
[ 8.696080] exynos-bus: new bus device registered: soc:bus-fsys-apb
(111000 KHz ~ 222000 KHz)
[ 8.706590] exynos-bus: new bus device registered: soc:bus-fsys2 (
75000 KHz ~ 200000 KHz)
[ 8.717661] exynos-bus: new bus device registered: soc:bus-mfc (
83250 KHz ~ 333000 KHz)
[ 8.728139] exynos-bus: new bus device registered: soc:bus-gen (
88700 KHz ~ 266000 KHz)
[ 8.737551] exynos-bus: new bus device registered: soc:bus-peri (
66600 KHz ~ 66600 KHz)
[ 8.748625] exynos-bus: new bus device registered: soc:bus-g2d (
83250 KHz ~ 333000 KHz)
[ 8.759427] exynos-bus: new bus device registered: soc:bus-g2d-acp (
66500 KHz ~ 266000 KHz)
[ 8.770366] exynos-bus: new bus device registered: soc:bus-jpeg (
75000 KHz ~ 300000 KHz)
[ 8.781135] exynos-bus: new bus device registered: soc:bus-jpeg-apb (
83250 KHz ~ 166500 KHz)
[ 8.791366] exynos-bus: new bus device registered: soc:bus-disp1-fimd
(120000 KHz ~ 200000 KHz)
[ 8.802418] exynos-bus: new bus device registered: soc:bus-disp1
(120000 KHz ~ 300000 KHz)
[ 8.813050] exynos-bus: new bus device registered:
soc:bus-gscl-scaler (150000 KHz ~ 300000 KHz)
[ 8.825308] exynos-bus: new bus device registered: soc:bus-mscl (
84000 KHz ~ 666000 KHz)
----------------------------------------------------------
It's true that they will not affect thermal zones, but unnecessarily,
they all will show up in the /sys/class/thermal/ as
thermal-devfreq-X
IMO the devfreq shouldn't be tight with devfreq cooling thermal.
The energy model is tied with a cooling device initialization.
So if we want to do power limitation, the energy model must be
initialized with the device, thus the cooling device also.
That is the reason why I'm ending up with this change. Chanwoo
suggestion makes sense and that will allow to move the initialization to
devfreq which is more sane but it does not solve the initial problem
with the energy model.
Make sense, the 'is_cooling_device' does the job.
Regards,
Lukasz
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