Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Mon, 27 Jul 2020 15:48:39 +0200 | Subject | Re: [PATCH v2 1/7] cpufreq: move invariance setter calls in cpufreq core |
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On Wed, Jul 22, 2020 at 11:38 AM Ionela Voinescu <ionela.voinescu@arm.com> wrote: > > From: Valentin Schneider <valentin.schneider@arm.com> > > 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 which is handled separately. > > Therefore, the hook works on the assumption 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, > gx-suspmod.c:439:2: .target = cpufreq_gx_target, > pcc-cpufreq.c:573:2: .target = pcc_cpufreq_target,
Also intel_pstate in the passive mode.
> > Should we care about drivers using this hook, we may be able to exploit > cpufreq_freq_transition_{being, end}(). This is handled in a separate > patch. > > 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. > > 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. > > As a result of setting the frequency scale factor in cpufreq core, after > callbacks that lend themselves to trigger it, remove this functionality > from the driver side. > > To be noted that despite marking a successful frequency change, many > cpufreq drivers will consider the new frequency as the requested > frequency, although this is might not be the one granted by the hardware. > > Therefore, the call to arch_set_freq_scale() is a "best effort" one, and > it is up to the architecture if the new frequency is used in the new > frequency scale factor setting (determined by the implementation of > arch_set_freq_scale()) or eventually used by the scheduler (determined > by the implementation of arch_scale_freq_capacity()). The architecture > is in a better position to decide if it has better methods to obtain > more accurate information regarding the current frequency and use that > information instead (for example, the use of counters). > > Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> > Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com> > Cc: Rafael J. Wysocki <rjw@rjwysocki.net> > Cc: Viresh Kumar <viresh.kumar@linaro.org> > --- > drivers/cpufreq/cpufreq-dt.c | 10 +--------- > drivers/cpufreq/cpufreq.c | 20 +++++++++++++++++--- > drivers/cpufreq/qcom-cpufreq-hw.c | 9 +-------- > drivers/cpufreq/scmi-cpufreq.c | 12 ++---------- > drivers/cpufreq/scpi-cpufreq.c | 6 +----- > drivers/cpufreq/vexpress-spc-cpufreq.c | 5 ----- > 6 files changed, 22 insertions(+), 40 deletions(-) > > diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c > index 944d7b45afe9..9fd4ce774f12 100644 > --- a/drivers/cpufreq/cpufreq-dt.c > +++ b/drivers/cpufreq/cpufreq-dt.c > @@ -40,16 +40,8 @@ static int set_target(struct cpufreq_policy *policy, unsigned int index) > { > struct private_data *priv = policy->driver_data; > unsigned long freq = policy->freq_table[index].frequency; > - int ret; > - > - ret = dev_pm_opp_set_rate(priv->cpu_dev, freq * 1000); > > - if (!ret) { > - arch_set_freq_scale(policy->related_cpus, freq, > - policy->cpuinfo.max_freq); > - } > - > - return ret; > + return dev_pm_opp_set_rate(priv->cpu_dev, freq * 1000); > } > > /* > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index 036f4cc42ede..bac4101546db 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -2058,9 +2058,16 @@ 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) > + arch_set_freq_scale(policy->related_cpus, freq, > + policy->cpuinfo.max_freq);
Why can't arch_set_freq_scale() handle freq == 0?
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