On Mon, Jan 08, 2018 at 12:21:17PM +0530, Viresh Kumar wrote:
On 08-01-18, 12:56, Leo Yan wrote:
I may not be suitable person to answser this; just give some background info for this:
I remembered Dietmar used Jankbench for comparing WALT and PELT, the scheduler signals have quite different effect on different testing case. Jankbench's tasks workload I think it's more related with responsiveness but from my understanding PCMark testing case is more related with sustainable workload?
Before I even observed the PELT signal (32ms period) might have better performance result than WALT for the sustainable workload, this is because the PELT signal has much longer decay time so it's more stable than WALT for some special case.
Sure, and the same reason can be used to argue against using WALT as that will have the same (bad) effects ?
I think so.
And I am not arguing on what's the best one for us here, but rather wanted to show that PELT can be modified with trivial changes to make it perform like WALT and maybe remove WALT support later on from Android as that is never going to be upstreamed.
Understand. I totally agree your testing is reasonable, WALT is mainly used to optimize UI responsiveness for better user experience; for this purpose there have many profiling on Uibench and Jankbench, so if the PELT optimization can achieve the similiar performance with WALT based on these test case, IMHO this will be more convienced.
- I saw you have disabled SchedTune for testing, but SchedTune is quite fatal for Jankbench (Or Uibench) testing. The 'prefer_idle' and boost margin have quite important effect, even WALT signal also need heavily to rely on these knobs for Jankbench tunning. E.g 'prefer_idle' is fatal for reducing janks for UI cases.
I didn't wanted any special effects to trick with my results and wanted least number of variables. I do believe that we will continue to use schedtune and that can be tuned to make WALT and PELT (8) behave in a similar way ?
Agree. Before SFO17 connect I profiled on Hikey960 with kernel 4.4, WALT with boosting margin 10% can get < 5% janks. PELT need improve boost margin to 15% or 20% to get similiar performance with WALT.
So If PELT can acheive same performance with WALT with same boosting margin, and if PELT can save power at the same time, this will be very nice :)
Just want to remind that besides the CPU frequency as one important metric, the "over-utilization" will be another important metric. I can see the PELT(8ms) can improve the performance result significantly, but not sure if this because the cpu util can easily reach to 80% tipping point so trigger "over-utilized" and finally boost performance by spreading tasks with SMP balance.
Thanks, Leo Yan