Messages in this thread | | | Date | Mon, 18 Sep 2023 23:09:13 +0530 | Subject | Re: [PATCH v3] sched/topology: remove sysctl_sched_energy_aware depending on the architecture | From | Shrikanth Hegde <> |
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On 9/18/23 5:52 PM, Valentin Schneider wrote: > On 15/09/23 23:40, Shrikanth Hegde wrote: >> On 9/15/23 5:30 PM, Valentin Schneider wrote: >>> On 14/09/23 23:26, Shrikanth Hegde wrote: >>>> On 9/14/23 9:51 PM, Valentin Schneider wrote: >>>>> On 13/09/23 17:18, Shrikanth Hegde wrote: >>>>>> sysctl_sched_energy_aware is available for the admin to disable/enable >>>>>> energy aware scheduling(EAS). EAS is enabled only if few conditions are >>>>>> met by the platform. They are, asymmetric CPU capacity, no SMT, >>>>>> valid cpufreq policy, frequency invariant load tracking. It is possible >>>>>> platform when booting may not have EAS capability, but can do that after. >>>>>> For example, changing/registering the cpufreq policy. >>>>>> >>>>>> At present, though platform doesn't support EAS, this sysctl is still >>>>>> present and it ends up calling rebuild of sched domain on write to 1 and >>>>>> NOP when writing to 0. That is confusing and un-necessary. >>>>>> >>>>> >>>> >>>> Hi Valentin, Thanks for taking a look at this patch. >>>> >>>>> But why would you write to it in the first place? Or do you mean to use >>>>> this as an indicator for userspace that EAS is supported? >>>>> >>>> >>>> Since this sysctl is present and its value being 1, it gives the >>>> impression to the user that EAS is supported when it is not. >>>> So its an attempt to correct that part. >>>> >>> >>> Ah, I see. Then how about just making the sysctl return 0 when EAS isn't >>> supported? And on top of it, prevent all writes when EAS isn't supported >>> (perf domains cannot be built, so there would be no point in forcing a >>> rebuild that will do nothing). >> >> Yes. That's another way. Thats what I had as possible approach in >> https://lore.kernel.org/lkml/d2c945d6-c4f0-a096-0623-731b11484f51@linux.vnet.ibm.com/ >> > > Thanks for the link; and apologies for bringing up topics that have been > discussed already. > >> >> >>> >>> I can never remember how to properly use the sysctl API, so that's a very >>> crude implementation, but something like so? >>> >>> --- >>> >>> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c >>> index 05a5bc678c089..dadfc5afc4121 100644 >>> --- a/kernel/sched/topology.c >>> +++ b/kernel/sched/topology.c >>> @@ -230,9 +230,28 @@ static int sched_energy_aware_handler(struct ctl_table *table, int write, >>> if (write && !capable(CAP_SYS_ADMIN)) >>> return -EPERM; >>> >>> + if (!sched_energy_enabled()) { >> >> Use of sched_energy_enabled won't work as Pierre has indicated. >> >> Instead this can be done by adding those checks in a helper function to >> do similar checks as done build_perf_domains. >> >> I can send v4 with this approach if it makes more sense. Please let me know. >> > > So what I'm thinking is the standard approach seems to be to keep the knobs > visible, but change how reads/writes to them are handled. > > For instance, SMT support has > > /sys/devices/system/cpu/smt > /control > /active > > And a system with CONFIG_HOTPLUG_SMT=y but no actual hardware SMT will > have: > > /control = notsupported > /active = 0 > > So IMO it would make sense to keep sched_energy_aware around, but make it > read 0 and prevent writes for systems that have the software support > compiled but don't have the actual hardware support.
ok.
> > In a pinch it also helps to know if CONFIG_ENERGY_MODEL was selected, > though that's obvious enough with CONFIG_SCHED_DEBUG=y. > ok. This would be simpler to implement as well. Removing it would have few tricky corner case scenarios as pierre has indicated.
Should be able to send out v4 sometime soon. I am on a holiday till Sep 19.
Pierre and Phil, thanks for the suggestions to commit message. I will incorporate the suggestions.
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