RPi3 Frequency Scaling

[robingroppe]

Just a question...
Is the limitation that the new cpu can only switch between 600 and 1200MHz hardware or software related?
Is it more efficient to ramp up to 1200MHz and finish the Task asap and sleep longer or lets say switch to 800MHz if thats sufficient for that given task?

[popcornmix]

The hardware and software supports arbitrary frequencies.
The ondemand governor we use by default just uses 600MHz and 1200MHz (on Pi3).
In general we believe it does not make sense to choose intermediate frequencies. When busy you may as well run as fast as you can, allowing the drop to the lower frequency sooner (and behaving more responsively for the user).

[robingroppe]

Okay. Can you give me a hint where to modify that?
I really want to check that.

[Ferroin]

Stupid question, but why is this apparently a hard coded policy in the driver? While I can understand the reasoning for this policy in general (the bit about responsiveness that is, I don't have enough information about the power consumption profiles of the CPU to render an opinion on the power savings from doing things this way), there are perfectly valid reasons for stepping the frequency up and down instead of just jumping between high and low, and while I can understand defaulting to a particular policy, it's kind of ridiculous that there isn't any way (at least from the documentation I've read) to change it from user space.

[robingroppe]

My hope is that this could also improve the temperature of the soc under moderate load.
Is there a way to modify this?

[popcornmix]

You can set, say arm_freq=850 into config.txt and reboot to see the effect of running at a lower max frequency is.
You can add additional frequencies to bcm2835_freq_table here:
https://github.com/raspberrypi/linux/blob/rpi-4.1.y/drivers/cpufreq/bcm2835-cpufreq.c
Or you can set the frequency explicity using the mailbox driver. E.g. source the following:

function vcmailbox()
{
  /opt/vc/bin/vcmailbox $*
}

function set_freq()
{
  local clock=$1
  local freq=$2   
  if [ $freq -le 1000000 ]; then
   let "freq *= 1000000"
  fi
  echo "set_freq($clock, $freq)"
  A=$(vcmailbox 0x00038002 12 8 $clock $freq 1)
}

then

pi@domnfs:~ $ echo performance | sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
pi@domnfs:~ $ set_freq 3 900
set_freq(3, 900000000)
pi@domnfs:~ $ vcgencmd measure_clock arm
frequency(45)=900000000

[robingroppe]

Okay. I have modified the freq_table and the kernel is building. Fingers crossed i got the table right.

[robingroppe]

Nope, got it wrong.
How is this supposed to look?

static struct cpufreq_frequency_table bcm2835_freq_table[] = {
{0, 0, 0},
{0, 0, 0},
{0, 0, CPUFREQ_TABLE_END},
};

[EDIT] Some folks on #raspberrypi irc said that this is not possible due to missing firmware headers from the foundation.

[popcornmix]

Lot of info here: https://github.com/raspberrypi/linux/tree/rpi-4.1.y/Documentation/cpu-freq

[robingroppe]

Yes i read that already. But still not smarter. ;)
Am 10.03.2016 20:46 schrieb "popcornmix" notifications@github.com:

Lot of info here:
https://github.com/raspberrypi/linux/tree/rpi-4.1.y/Documentation/cpu-freq

—
Reply to this email directly or view it on GitHub
#1335 (comment).

[clivem]

@popcornmix I know this isn't pretty, it's a quick 30 second hack patch, (was just intended to give @robingroppe a pointer), adding an intermediate 900MHz op point. But it doesn't actually work as intended..... It seems that with the first call via firmware to set 900MHz speed, that and every subsequent attempt to set freq via firmware mailbox to a value <1.2GHz, returns 1.2GHz actual. Any ideas?

rpi-kernel-cpufreq-hack-patch.txt

bcm2835_cpufreq_module_init:127: IN
bcm2835-cpufreq:bcm2835_cpufreq_get_clock:115: Min frequency = 600000
bcm2835-cpufreq:bcm2835_cpufreq_get_clock:115: Max frequency = 1200000
bcm2835-cpufreq: min=600000 mid=900000 max=1200000
bcm2835-cpufreq:bcm2835_cpufreq_get_clock:115: Current frequency = 600000
bcm2835-cpufreq:bcm2835_cpufreq_driver_get:200: cpu0: freq=600000
bcm2835-cpufreq:bcm2835_cpufreq_set_clock:94: Setting new frequency = 600000 -> 1200000 (actual 1200000)
bcm2835-cpufreq:bcm2835_cpufreq_driver_target_index:187: ondemand: 2: freq 600000->1200000
bcm2835-cpufreq:bcm2835_cpufreq_set_clock:94: Setting new frequency = 1200000 -> 900000 (actual 1200000)
bcm2835-cpufreq:bcm2835_cpufreq_driver_target_index:187: ondemand: 1: freq 1200000->1200000
bcm2835-cpufreq:bcm2835_cpufreq_set_clock:94: Setting new frequency = 900000 -> 600000 (actual 1200000)
bcm2835-cpufreq:bcm2835_cpufreq_driver_target_index:187: ondemand: 0: freq 900000->1200000
bcm2835-cpufreq:bcm2835_cpufreq_set_clock:94: Setting new frequency = 600000 -> 900000 (actual 1200000)
bcm2835-cpufreq:bcm2835_cpufreq_driver_target_index:187: ondemand: 1: freq 600000->1200000
bcm2835-cpufreq:bcm2835_cpufreq_set_clock:94: Setting new frequency = 900000 -> 600000 (actual 1200000)
bcm2835-cpufreq:bcm2835_cpufreq_driver_target_index:187: ondemand: 0: freq 900000->1200000
bcm2835-cpufreq:bcm2835_cpufreq_set_clock:94: Setting new frequency = 600000 -> 900000 (actual 1200000)
bcm2835-cpufreq:bcm2835_cpufreq_driver_target_index:187: ondemand: 1: freq 600000->1200000

[Ruffio]

@robingroppe has your issue been resolved? If so, please close this issue. Thanks.

[buxit]

i agree that the kernel should expose more frequencies. the cpufreq_userspace governor is useful in some situations.

@popcornmix your vcmailbox snippet is great and works as expected. where can i find a list of all possible (settable) $clocks?

during normal use i need about 700MHz to sustain a 60Hz framerate. at this clock speed the temperature stays below 80°C, even with an enclosure. on rare occasions and for rather short periods (during calibration) i want the cpu to work as fast as possible. the default ondemand setting would keep the cpu running at 1.2GHz at all times.

i'd like to additionally experiment with different gpu / ram frequencies if possible and stable.

[popcornmix]

@buxit see https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface

[robingroppe]

The race to idle strategy may be valid for tasks that can be finished but if you have an endless task it would be better not to ramp up to full freq.
Totally forgot this issue. I would still love to see this working out.

[JamesH65]

Closing due to lack of activity. Reopen if you feel this issue is still relevant.
Closing this issue as questions answered/resolved.

[Kungergely]

I'm experiencing an issue with a RPi3 where the system seems to insist on running at 600 MHz instead of the 1.2 GHz base frequency every time a USB device is plugged in. The workaround of writing 1200000 to /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq seems to help somewhat, but when trying to run vcmailbox it fails with the following error message:
./vcmailbox 0x00038002 12 8 3 900
ioctl_set_msg failed:-1
0x00000020 0x00000000 0x00038002 0x0000000c 0x00000008 0x00000003 0x000004b0 0x00000000

Any hints on why is this happening?

[pelwell]

What does vcgencmd get_throttled report?

[saikat007]

@popcornmix @clivem Is it possible to scale the CPU core voltage as well after the booting process, let's say using some shell commands similar to how we can switch frequency? For example, I want to lower the CPU voltage from 1.2V(default) to 1.1V, Is there a way to do it using some tool or from the terminal by changing some file in /sys (instead of using over_voltage in /boot/config)? I am using a Raspberry Pi 3B+ device.