11.06.2021 12:52, Daniel Lezcano пишет: > On 14/05/2021 23:16, Michał Mirosław wrote: >> On Mon, May 10, 2021 at 11:25:53PM +0300, Dmitry Osipenko wrote: >>> It's possible to hit the temperature of the thermal zone in a very warm >>> environment under a constant load, like watching a video using software >>> decoding. It's even easier to hit the limit with a slightly overclocked >>> CPU. Bump the temperature limit by 10C in order to improve user >>> experience. Acer A500 has a large board and 10" display panel which are >>> used for the heat dissipation, the SoC is placed far away from battery, >>> hence we can safely bump the temperature limit. >> >> 60^C looks like a touch-safety limit (to avoid burns for users). Did you >> verify the touchable parts' temperature somehow after the change? > > The skin temperature and the CPU/GPU etc ... temperatures are different > things. > > For the embedded system there is the dissipation system and a > temperature sensor on it which is the skin temp. This temperature is the > result of the heat of all the thermal zones on the board and must be > below 45°C. The temperature slowly changes. > > On the CPU, the temperature changes can be very fast and you have to > take care of keeping it below the max temperature specified in the TRM > by using different techniques (freq changes, idle injection, ...) but > the temperature can be 75°C, 85°C or whatever the manual says. > > 50°C and 60°C are low temperature for a CPU and that will inevitably > impact the performances, so setting the temperature close the max > temperature is what will allow max performances. > > What matters is the skin temperature. > > The skin temperature must be monitored by other techniques, eg. using > the TDP of the system and throttle the different devices to keep them in > this power budget. That is the role of an thermal daemon. Thank you for the clarification. Indeed, I wasn't sure how to make use of the skin temperature properly. The skin temperature varies a lot depending on the thermal capabilities of a particular device. It's about 15C below CPU core at a full load on A500, while it's 2C below CPU core on Nexus 7. But this is expected since Nexus 7 can't dissipate heat efficiently. I will revisit the DT thermal zones again for the next kernel release.
