Messages in this thread | | | Date | Wed, 6 Sep 2023 23:13:01 +0200 | Subject | Re: [RFC PATCH 5/7] sched/schedutil: Add a new tunable to dictate response time | From | Dietmar Eggemann <> |
| |
On 28/08/2023 01:32, Qais Yousef wrote:
[...]
> @@ -427,6 +427,23 @@ This governor exposes only one tunable: > The purpose of this tunable is to reduce the scheduler context overhead > of the governor which might be excessive without it. > > +``respone_time_ms`` > + Amount of time (in milliseconds) required to ramp the policy from > + lowest to highest frequency. Can be decreased to speed up the > + responsiveness of the system, or increased to slow the system down in > + hope to save power. The best perf/watt will depend on the system > + characteristics and the dominant workload you expect to run. For > + userspace that has smart context on the type of workload running (like > + in Android), one can tune this to suite the demand of that workload. > + > + Note that when slowing the response down, you can end up effectively > + chopping off the top frequencies for that policy as the util is capped > + to 1024. On HMP systems where some CPUs have a capacity less than 1024,
HMP isn't used in mainline AFAIK. IMHO, the term `asymmetric CPU capacity` systems is used.
[...]
> @@ -59,6 +61,45 @@ static DEFINE_PER_CPU(struct sugov_cpu, sugov_cpu); > > /************************ Governor internals ***********************/ > > +static inline u64 sugov_calc_freq_response_ms(struct sugov_policy *sg_policy) > +{ > + int cpu = cpumask_first(sg_policy->policy->cpus); > + unsigned long cap = capacity_orig_of(cpu); > + > + return approximate_runtime(cap); > +}
I can see the potential issue of schedutil being earlier initialized than the `max frequency scaling of cpu_capacity_orig` happens in drivers/base/arch_topology.c.
So the response_time_ms setup for a little CPU on Juno-r0 wouldn't happen on cpu_capacity_orig = 446 -> 26ms but on on the raw capacity value from dt:
capacity-dmips-mhz = <578>
So I would expect to see t = 32ms * ln(1 - 578/1024)/ln(0.5) = 38ms instead.
We have a similar dependency between `max frequency scaled cpu_capacity_orig` and the EM setup code.
[...]
| |