On 01-07-20, 10:07, Ionela Voinescu wrote: > From: Valentin Schneider <[email protected]> > > To properly scale its per-entity load-tracking signals, the task scheduler > needs to be given a frequency scale factor, i.e. some image of the current > frequency the CPU is running at. Currently, this scale can be computed > either by using counters (APERF/MPERF on x86, AMU on arm64), or by > piggy-backing on the frequency selection done by cpufreq. > > For the latter, drivers have to explicitly set the scale factor > themselves, despite it being purely boiler-plate code: the required > information depends entirely on the kind of frequency switch callback > implemented by the driver, i.e. either of: target_index(), target(), > fast_switch() and setpolicy(). > > The fitness of those callbacks with regard to driving the Frequency > Invariance Engine (FIE) is studied below: > > target_index() > ============== > Documentation states that the chosen frequency "must be determined by > freq_table[index].frequency". It isn't clear if it *has* to be that > frequency, or if it can use that frequency value to do some computation > that ultimately leads to a different frequency selection. All drivers > go for the former, while the vexpress-spc-cpufreq has an atypical > implementation. > > Thefore, the hook works on the asusmption the core can use > freq_table[index].frequency. > > target() > ======= > This has been flagged as deprecated since: > > commit 9c0ebcf78fde ("cpufreq: Implement light weight ->target_index() > routine") > > It also doesn't have that many users: > > cpufreq-nforce2.c:371:2: .target = nforce2_target, > cppc_cpufreq.c:416:2: .target = cppc_cpufreq_set_target, > pcc-cpufreq.c:573:2: .target = pcc_cpufreq_target, > > Should we care about drivers using this hook, we may be able to exploit > cpufreq_freq_transition_{being, end}(). Otherwise, if FIE support is > desired in their current state, arch_set_freq_scale() could still be > called directly by the driver, while CPUFREQ_CUSTOM_SET_FREQ_SCALE > could be used to mark support for it. > > fast_switch() > ============= > This callback *has* to return the frequency that was selected. > > setpolicy() > =========== > This callback does not have any designated way of informing what was the > end choice. But there are only two drivers using setpolicy(), and none > of them have current FIE support: > > drivers/cpufreq/longrun.c:281: .setpolicy = longrun_set_policy, > drivers/cpufreq/intel_pstate.c:2215: .setpolicy = > intel_pstate_set_policy, > > The intel_pstate is known to use counter-driven frequency invariance.
Same for acpi-cpufreq driver as well ? And I think we should do the freq-invariance thing for all the above categories nevertheless. > If FIE support is desired in their current state, arch_set_freq_scale() > could still be called directly by the driver, while > CPUFREQ_CUSTOM_SET_FREQ_SCALE could be used to mark support for it. > > Conclusion > ========== > > Given that the significant majority of current FIE enabled drivers use > callbacks that lend themselves to triggering the setting of the FIE scale > factor in a generic way, move the invariance setter calls to cpufreq core, > while filtering drivers that flag custom support using > CPUFREQ_CUSTOM_SET_FREQ_SCALE. > > Signed-off-by: Valentin Schneider <[email protected]> > Signed-off-by: Ionela Voinescu <[email protected]> > Cc: Rafael J. Wysocki <[email protected]> > Cc: Viresh Kumar <[email protected]> > --- > drivers/cpufreq/cpufreq.c | 20 +++++++++++++++++--- > 1 file changed, 17 insertions(+), 3 deletions(-) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index 0128de3603df..83b58483a39b 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -2046,9 +2046,16 @@ EXPORT_SYMBOL(cpufreq_unregister_notifier); > unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy, > unsigned int target_freq) > { > + unsigned int freq; > + > target_freq = clamp_val(target_freq, policy->min, policy->max); > + freq = cpufreq_driver->fast_switch(policy, target_freq); > + > + if (freq && !(cpufreq_driver->flags & CPUFREQ_CUSTOM_SET_FREQ_SCALE)) > + arch_set_freq_scale(policy->related_cpus, freq, > + policy->cpuinfo.max_freq); This needs to be a separate function. > > - return cpufreq_driver->fast_switch(policy, target_freq); > + return freq; > } > EXPORT_SYMBOL_GPL(cpufreq_driver_fast_switch); > > @@ -2140,7 +2147,7 @@ int __cpufreq_driver_target(struct cpufreq_policy > *policy, > unsigned int relation) > { > unsigned int old_target_freq = target_freq; > - int index; > + int index, retval; > > if (cpufreq_disabled()) > return -ENODEV; > @@ -2171,7 +2178,14 @@ int __cpufreq_driver_target(struct cpufreq_policy > *policy, > > index = cpufreq_frequency_table_target(policy, target_freq, relation); > > - return __target_index(policy, index); > + retval = __target_index(policy, index); > + > + if (!retval && !(cpufreq_driver->flags & CPUFREQ_CUSTOM_SET_FREQ_SCALE)) > + arch_set_freq_scale(policy->related_cpus, > + policy->freq_table[index].frequency, policy->cur gets updated for both target and target_index type drivers. You can use that safely. It gets updated after the postchange notification. > + policy->cpuinfo.max_freq); > + > + return retval; > } > EXPORT_SYMBOL_GPL(__cpufreq_driver_target); -- viresh
