Messages in this thread | | | Date | Sat, 10 Jun 2023 12:24:39 -0500 | Subject | Re: [PATCH 1/1] thermal: sysfs: avoid actual readings from sysfs | From | Russell Haley <> |
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On 6/7/23 11:38, Eduardo Valentin wrote: >> Can you elaborate 'the timing requirement for the governors' ? I'm >> missing the point > > > The point is to avoid contention on the device update path. > Governor that use differential equations on temperature over time > will be very time sensitive. Step wise, power allocator, or any > PID will be very sensitive to time. So, If userspace is hitting > this API too often we can see cases where the updates needed to > service userspace may defer/delay the execution of the governor > logic. > > Despite that, there is really no point to have more updates than > what was configured for the thermal zone to support. Say that > we configure a thermal zone to update itself every 500ms, yet > userspace keeps sending reads every 100ms, we do not need necessarily > to do a trip to the device every single time to update the temperature, > as per the design for the thermal zone.
A userspace governor might *also* use PID or filter multiple samples taken at high rate. I specifically switched my python fan control script from the Intel coretemp hwmon to the x86_pkg_tmp thermal zone because of the coretemp driver's annoying 1-second caching behavior.
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