Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Thu, 3 Dec 2020 15:44:04 +0100 | Subject | Re: [RFC][PATCH 1/2] cpufreq: Add special-purpose fast-switching callback for drivers |
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On Thu, Dec 3, 2020 at 1:42 PM Peter Zijlstra <peterz@infradead.org> wrote: > > On Mon, Nov 30, 2020 at 07:37:01PM +0100, Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > > > First off, some cpufreq drivers (eg. intel_pstate) can pass hints > > beyond the current target frequency to the hardware and there are no > > Everything CPPC, which is quite a bit these days.
Right, but that is still "some". :-) I can add it to the list of examples, though.
> > + /* > > + * ->fast_switch() replacement for drivers that use an internal > > + * representation of performance levels and can pass hints other than > > + * the target performance level to the hardware. > > + */ > > + void (*adjust_perf)(unsigned int cpu, bool busy, > > + unsigned long min_perf, > > + unsigned long target_perf, > > + unsigned long capacity); > > > > I'm not sure @busy makes sense, that's more a hack because @util had a > dip and should remain inside schedutil.
So I did it this way, because schedutil would need to store the old value of target_perf for this and intel_pstate already does that.
But if a new util_hook is used in this case, the existing space in sg_policy may be used for that.
> > @@ -454,6 +455,25 @@ static void sugov_update_single(struct u > > util = sugov_get_util(sg_cpu); > > max = sg_cpu->max; > > util = sugov_iowait_apply(sg_cpu, time, util, max); > > + > > + /* > > + * This code runs under rq->lock for the target CPU, so it won't run > > + * concurrently on two different CPUs for the same target and it is not > > + * necessary to acquire the lock in the fast switch case. > > + */ > > + if (sg_policy->direct_fast_switch) { > > + /* > > + * In this case, any optimizations that can be done are up to > > + * the driver. > > + */ > > + cpufreq_driver_adjust_perf(sg_cpu->cpu, > > + sugov_cpu_is_busy(sg_cpu), > > + map_util_perf(sg_cpu->bw_dl), > > + map_util_perf(util), max); > > + sg_policy->last_freq_update_time = time; > > + return; > > + } > > Instead of adding more branches, would it makes sense to simply set a > whole different util_hook in this case?
Looks doable without too much code duplication. Lemme try.
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