On 04/24/2019 11:57 AM, Ionela Voinescu wrote: > Hi Thara, > > The idea and the results look promising. I'm trying to understand better > the cause of the improvements so I've added below some questions that > would help me out with this.
Hi Ionela, Thanks for the review. > > >> Regarding testing, basic build, boot and sanity testing have been >> performed on hikey960 mainline kernel with debian file system. >> Further, aobench (An occlusion renderer for benchmarking realworld >> floating point performance), dhrystone and hackbench test have been >> run with the thermal pressure algorithm. During testing, due to >> constraints of step wise governor in dealing with big little systems, >> cpu cooling was disabled on little core, the idea being that >> big core will heat up and cpu cooling device will throttle the >> frequency of the big cores there by limiting the maximum available >> capacity and the scheduler will spread out tasks to little cores as well. >> Finally, this patch series has been boot tested on db410C running v5.1-rc4 >> kernel. >> > > Did you try using IPA as well? It is better equipped to deal with > big-LITTLE systems and it's more probable IPA will be used for these > systems, where your solution will have the biggest impact as well. > The difference will be that you'll have both the big cluster and the > LITTLE cluster capped in different proportions depending on their > utilization and their efficiency. No. I did not use IPA simply because it was not enabled in mainline. I agree it is better equipped to deal with big-little systems. The idea to remove cpu cooling on little cluster was to in some (not the cleanest) manner to mimic this. But I agree that IPA testing is possibly the next step.Any help in this regard is appreciated. > >> During the course of development various methods of capturing >> and reflecting thermal pressure were implemented. >> >> The first method to be evaluated was to convert the >> capped max frequency into capacity and have the scheduler use the >> instantaneous value when updating cpu_capacity. >> This method is referenced as "Instantaneous Thermal Pressure" in the >> test results below. >> >> The next two methods employs different methods of averaging the >> thermal pressure before applying it when updating cpu_capacity. >> The first of these methods re-used the PELT algorithm already present >> in the kernel that does the averaging of rt and dl load and utilization. >> This method is referenced as "Thermal Pressure Averaging using PELT fmwk" >> in the test results below. >> >> The final method employs an averaging algorithm that collects and >> decays thermal pressure based on the decay period. In this method, >> the decay period is configurable. This method is referenced as >> "Thermal Pressure Averaging non-PELT Algo. Decay : XXX ms" in the >> test results below. >> >> The test results below shows 3-5% improvement in performance when >> using the third solution compared to the default system today where >> scheduler is unware of cpu capacity limitations due to thermal events. >> > > Did you happen to record the amount of capping imposed on the big cores > when these results were obtained? Did you find scenarios where the > capacity of the bigs resulted in being lower than the capacity of the > LITTLEs (capacity inversion)? > This is one case where we'll see a big impact in considering thermal > pressure. I think I saw capacity inversion in some scenarios. I did not particularly capture them. > > Also, given that these are more or less sustained workloads, I'm > wondering if there is any effect on workloads running on an uncapped > system following capping. I would image such a test being composed of a > single threaded period (no capping) followed by a multi-threaded period > (with capping), continued in a loop. It might be interesting to have > something like this as well, as part of your test coverage I do not understand this. There is either capping for a workload or no capping. There is no sysctl entry to turn on or off capping. Regards Thara > > > Thanks, > Ionela. > -- Regards Thara
