Messages in this thread Patch in this message | | | Date | Fri, 15 Sep 2023 15:35:58 +0200 | Subject | Re: [PATCH v3] sched/topology: remove sysctl_sched_energy_aware depending on the architecture | From | Pierre Gondois <> |
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Hello Valentin,
On 9/15/23 14:00, 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).
I think the issue comes from the fact there is no variable representing whether EAS is supported or not. sched_energy_enabled()/sched_energy_present tells whether EAS is actively running on the system instead.
So on a system with EAS running, I think what would happen is: # Disable EAS and set sched_energy_present=0 echo 0 > /proc/sys/kernel/sched_energy_aware
# sched_energy_present==0, so we get -EOPNOTSUPP echo 1 > /proc/sys/kernel/sched_energy_aware
> > 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()) { > + if (write) > + return -EOPNOTSUPP; > + else { > + size_t len; > + > + if (*ppos) { > + *lenp = 0; > + return 0; > + } > + > + len = snprintf((char *)buffer, 3, "0\n"); > + > + *lenp = len; > + *ppos += len; > + return 0; > + } > + } > + > ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); > if (!ret && write) { > - state = static_branch_unlikely(&sched_energy_present); > + state = sched_energy_enabled(); > if (state != sysctl_sched_energy_aware) > rebuild_sched_domains_energy(); > } >
Regards, Pierre
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