On Fri, Oct 28, 2016 at 12:55:52AM -0700, Vikram Mulukutla wrote: > On 2016-10-28 00:29, Peter Zijlstra wrote: > >On Fri, Oct 28, 2016 at 12:10:39AM -0700, Vikram Mulukutla wrote: > >> > >>We propose Window-Assisted Load Tracking (WALT) as an alternative or > >>additional load tracking scheme in lieu of or along with PELT, one > >>that in our estimation better tracks task demand and CPU utilization > >>especially for use cases on mobile devices. WALT was conceived by > >>Srivatsa Vaddagiri to provide better perf-per-watt numbers on > >>asymmetric CPU (frequency and/or IPC) implementations, (specifically > >>on Qualcomm Snapgdragon chipsets running Android) and its metrics > >>have been used to guide task placement and p-state selection (load > >>balancing in CFS still uses PELT statistics). WALT is now present in > >>the android-common kernel as well. > > > >And how come we only learn of it after its already shipping? Isn't that > >arse backwards? > > Yes, but also we were not confident that it would be close to being > acceptable > upstream since it was intricately tied to our HMP scheduler. However now > that > more parties including the folks at ARM are interested, and given that EAS > exists and schedutil was merged into mainline, we felt it the right time > to try and introduce the concept. In general we are seriously trying to get > more things upstream and converge.
That's good to hear, great! That said, I would much prefer to modify/augment existing PELT stuff than to add an entirely new set of accounting on the side of it. But yes, I (and others) are aware of the pain points you mentioned with using the PELT signal for schedutil. We'll have to see what we can come up with.
