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The Natural Philosopher <
tnp@invalid.invalid> wrote:
> > The Pi 4B will definitely throttle with only a ventilated case if it is
> > anything other than sitting idle all the time.
> >
> I am not interested in proof by assertion
> I had mine up to 130% on `top` and it never made more than 76┬░C
You do know that `top` won`t show throttling? Throttling means the CPU is
clocked lower than the maximum frequency to reduce heat generation - top
will still show `100%` of CPU (for one core) but that will be 100% of a
lower clock speed.
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
shows you the current clock of CPU core 0 and:
sudo vcgencmd get_throttled
will tell you the throttling status:
#### get_throttled
Returns the throttled state of the system. This is a bit pattern.
| Bit | Meaning |
|:---:|---------|
| 0 | Under-voltage detected |
| 1 | Arm frequency capped |
| 2 | Currently throttled |
| 3 | Soft temperature limit active |
| 16 | Under-voltage has occurred |
| 17 | Arm frequency capped has occurred |
| 18 | Throttling has occurred |
| 19 | Soft temperature limit has occurred
For example if I run `stress -c 4` then get_throttled gives me:
throttled=0xe0008
so the temperature limit is in operation and throttling has occurred in the
past. (this Pi4 has cooling, I can`t remember but I think there`s a
heatsink and fan in there)
$ sudo vcgencmd measure_temp
temp=84.7`C
so it`s up near its thermal limit.
> > I don`t see the point of letting it throttling when an inexpensive fan
> > will keep it at full speed under any load.
> >
> I question that it will in fact throttle.
>
> Like so much `everybody knows` when you look at it it is in fact
> `everyone believes because people selling fans told them so.
`Everybody knows` because they have evidence, not assertions.
> The whole point of ARM is its lower power and lack of need for forced
> cooling
Everyone`s been thermally limited for maybe 15 years, it`s just that Arm
cores have traditionally targeted a lower thermal envelope in devices where
forced air cooling isn`t an option. The way this works is that CPUs work
until they hit their thermal envelope and then throttle. No popular
application processor for maybe a couple of decades has been able to power
all the silicon at once to max performance and stay within the thermal
budget.
Theo
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