On 11/21/2019 09:38 AM, Amit Kucheria wrote: > On Thu, Nov 21, 2019 at 7:40 PM Thara Gopinath > <thara.gopinath@xxxxxxxxxx> wrote: >> >> On 11/21/2019 12:50 AM, Amit Kucheria wrote: >>> From: Ram Chandrasekar <rkumbako@xxxxxxxxxxxxxx> >>> >>> Currently, step wise governor increases the mitigation when the >>> temperature goes above a threshold and decreases the mitigation when the >>> temperature goes below the threshold. If there is a case where the >>> temperature is wavering around the threshold, the mitigation will be >>> applied and removed every iteration, which is not very efficient. >>> >>> The use of hysteresis temperature could avoid this ping-pong of >>> mitigation by relaxing the mitigation to happen only when the >>> temperature goes below this lower hysteresis value. >> Hi Amit, >> >> Can this not lead to ping-pong around the hysteresis temperature? > > That isn't how hysteresis is supposed to work if there is a sufficient > delta between your trip point and your hysteresis value. > > e.g. if you have a trip at 80C and a hysteresis of 10C, it means that > you will start throttling at 80C, but you won't STOP throttling until > you cool down to 70C. At that point, you will wait again to get to 80C > before throttling again. > IOW, on the downward slope (80 -> 70) you still have throttling active > and on the upward slope (70 -> 80), you have no[1] throttling, so > different behaviour is the same temperature range depending on > direction. > > If your hysteresis value was very low .e.g. 1C, it would certainly be useless. Thanks for the explanation. I think averaging can still give a smoother experience/transition. But then it has to be implemented and tested against this solution. Other reason for this solution is hysteresis can be a higher value if needed where as averaging might not give that flexibility. I have some other comments on the patch which I have posted separately. > >> If the idea is to minimize ping-pong isn't average a better method? > > We shouldn't ping-pong with the asymmetric behaviour described above. > > Regards, > Amit > [1] This is a simple example with a single trip point. > -- Warm Regards Thara
