Messages in this thread | | | Date | Fri, 23 Mar 2018 23:06:11 -0700 | Subject | Re: [RFC PATCH 5/6] sched/fair: Select an energy-efficient CPU on task wake-up | From | Joel Fernandes <> |
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On March 23, 2018 6:34:22 PM PDT, Quentin Perret <quentin.perret@arm.com> wrote: >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 ?
Yeah definitely. Go for it.
- Joel
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