Hi Dietmar On Fri, Apr 2, 2021 at 2:07 AM Dietmar Eggemann <dietmar.eggem...@arm.com> wrote: > > +cc: Pierre Gondois <pierre.gond...@arm.com> > > On 30/03/2021 11:45, Quentin Perret wrote: > > Hi, > > > > On Tuesday 30 Mar 2021 at 13:21:54 (+0800), Xuewen Yan wrote: > >> From: Xuewen Yan <xuewen....@unisoc.com> > >> > >> now the energy delta compute as follow: > >> > >> base_energy_pd = compute_energy(p, -1, pd); > >> --->Traverse all CPUs in pd > >> --->em_pd_energy() > >> ----------------------------------------------------- \ > >> search for the max_sapre_cap_cpu \ > >> --------------------------------- search time > >> cur_delta = compute_energy(p, max_spare_cap_cpu, pd); / > >> --->Traverse all CPUs in pd / > >> ---------------------------------------------------- / > >> --->em_pd_energy() > >> cur_delta -= base_energy_pd; > >> > >> During the search_time, or when calculate the cpu_util in > >> compute_energy(), there may occurred task dequeue or cpu_util change, > >> it may cause the cur_energy < base_energy_pd, so the cur_delta > >> would be negative. But the cur_delta is unsigned long, at this time, > >> the cur_delta would always bigger than best_delta of last pd. > >> > >> Change the vars to signed long. > > > > Is that really helping though? > > > > Yes you will not overflow, but the decision is still 'wrong' if the util > > values are not stable for the entire wake-up. I think folks on the Arm > > side had patches to try and cache the util values upfront, and then use > > them throughout feec() and compute_energy(), which I think would be a > > better fix. > > > > Dietmar, wdyt? > > Yes, we have some patches from Pierre Gondois which introduce a pd cache > to store the CPU utilization values so they can be reused for 'cpu != > dst_cpu' calculations within find_energy_efficient_cpu() (feec()). > > We did run them in our Jan 2021 EAS integration: > > https://gitlab.arm.com/linux-arm/linux-power/-/commits/eas/next/integration-20210129 > > sched: Allocate pd_cache when EAS is enabled > sched/fair: Use pd_cache to speed up find_energy_efficient_cpu() > > We haven't posted them since we're still looking for a story to justify > the extra complexity. The experiments on Arm64 Juno (2 big, 4 little > CPUs) showed 1-2% failure due to changes of CPU utilization values > during feec(). There was a 5% (big CPU)-10% (little CPU) runtime > reduction for feec() with the patches.
I test the patch, but the overflow still exists. In the "sched/fair: Use pd_cache to speed up find_energy_efficient_cpu()" I wonder why recompute the cpu util when cpu==dst_cpu in compute_energy(), when the dst_cpu's util change, it also would cause the overflow. Thanks
