Messages in this thread | | | Date | Sat, 24 Mar 2018 01:34:22 +0000 | From | Quentin Perret <> | Subject | Re: [RFC PATCH 5/6] sched/fair: Select an energy-efficient CPU on task wake-up |
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On Friday 23 Mar 2018 at 18:13:56 (-0700), Joel Fernandes wrote: > Hi Morten, > > On Fri, Mar 23, 2018 at 8:47 AM, Morten Rasmussen > <morten.rasmussen@arm.com> wrote: > > On Thu, Mar 22, 2018 at 01:10:22PM -0700, Joel Fernandes wrote:
[...]
> > You mean if SD_BALANCE_WAKE isn't set on sched_domains? > > Yes. > > > The current code seems to rely on that flag to be set to work correctly. > > Otherwise, the loop might bail out on !want_affine and we end up doing > > the find_energy_efficient_cpu() on the lowest level sched_domain even if > > there is higher level one which isn't over-utilized. > > > > However, SD_BALANCE_WAKE should be set if SD_ASYM_CPUCAPACITY is set so > > sd == NULL shouldn't be possible? This only holds as long as we only > > want EAS for asymmetric systems. > > Yes, I see you had topology code that set SD_BALANCE_WAKE for ASYM. It > makes sense to me then, thanks for the clarification. > > Still I feel it is a bit tedious/confusing when reading code to draw > the conclusion about why sd is checked first before doing > find_energy_efficient_cpu (and that sd will != NULL for ASYM systems). > If energy_sd is set, then we can just proceed with EAS without > checking that sd != NULL. This function in mainline is already pretty > confusing as it is :-(
Right I see your point. The code is correct as is, but I agree that having a code structured as
if (energy_sd) { new_cpu = find_energy_efficient_cpu(energy_sd, p, prev_cpu); } else if (!sd) { ...
might be easier to understand and functionally equivalent. What do you think ?
Thanks, Quentin
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