Messages in this thread | | | From | Vincent Guittot <> | Date | Mon, 10 Oct 2022 11:32:28 +0200 | Subject | Re: [PATCH 2/2] cpufreq: Update CPU capacity reduction in store_scaling_max_freq() |
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On Mon, 10 Oct 2022 at 11:30, Lukasz Luba <lukasz.luba@arm.com> wrote: > > > > On 10/10/22 10:15, Vincent Guittot wrote: > > On Mon, 10 Oct 2022 at 11:02, Lukasz Luba <lukasz.luba@arm.com> wrote: > >> > >> > >> > >> On 10/10/22 06:39, Viresh Kumar wrote: > >>> Would be good to always CC Scheduler maintainers for such a patch. > >> > >> Agree, I'll do that. > >> > >>> > >>> On 30-09-22, 10:48, Lukasz Luba wrote: > >>>> When the new max frequency value is stored, the task scheduler must > >>>> know about it. The scheduler uses the CPUs capacity information in the > >>>> task placement. Use the existing mechanism which provides information > >>>> about reduced CPU capacity to the scheduler due to thermal capping. > >>>> > >>>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> > >>>> --- > >>>> drivers/cpufreq/cpufreq.c | 18 +++++++++++++++++- > >>>> 1 file changed, 17 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > >>>> index 1f8b93f42c76..205d9ea9c023 100644 > >>>> --- a/drivers/cpufreq/cpufreq.c > >>>> +++ b/drivers/cpufreq/cpufreq.c > >>>> @@ -27,6 +27,7 @@ > >>>> #include <linux/slab.h> > >>>> #include <linux/suspend.h> > >>>> #include <linux/syscore_ops.h> > >>>> +#include <linux/thermal.h> > >>>> #include <linux/tick.h> > >>>> #include <linux/units.h> > >>>> #include <trace/events/power.h> > >>>> @@ -718,6 +719,8 @@ static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf) > >>>> static ssize_t store_scaling_max_freq > >>>> (struct cpufreq_policy *policy, const char *buf, size_t count) > >>>> { > >>>> + unsigned int frequency; > >>>> + struct cpumask *cpus; > >>>> unsigned long val; > >>>> int ret; > >>>> > >>>> @@ -726,7 +729,20 @@ static ssize_t store_scaling_max_freq > >>>> return -EINVAL; > >>>> > >>>> ret = freq_qos_update_request(policy->max_freq_req, val); > >>>> - return ret >= 0 ? count : ret; > >>>> + if (ret >= 0) { > >>>> + /* > >>>> + * Make sure that the task scheduler sees these CPUs > >>>> + * capacity reduction. Use the thermal pressure mechanism > >>>> + * to propagate this information to the scheduler. > >>>> + */ > >>>> + cpus = policy->related_cpus; > >>> > >>> No need of this, just use related_cpus directly. > >>> > >>>> + frequency = __resolve_freq(policy, val, CPUFREQ_RELATION_HE); > >>>> + arch_update_thermal_pressure(cpus, frequency); > >>> > >>> I wonder if using the thermal-pressure API here is the right thing to > >>> do. It is a change coming from User, which may or may not be > >>> thermal-related. > >> > >> Yes, I thought the same. Thermal-pressure name might be not the > >> best for covering this use case. I have been thinking about this > >> thermal pressure mechanism for a while, since there are other > >> use cases like PowerCap DTPM which also reduces CPU capacity > >> because of power policy from user-space. We don't notify > >> the scheduler about it. There might be also an issue with virtual > >> guest OS and how that kernel 'sees' the capacity of CPUs. > >> We might try to use this 'thermal-pressure' in the guest kernel > >> to notify about available CPU capacity (just a proposal, not > >> even an RFC, since we are missing requirements, but issues where > >> discussed on LPC 2022 on ChromeOS+Android_guest) > > > > The User space setting scaling_max_freq is a long scale event and it > > should be considered as a new running environnement instead of a > > transient event. I would suggest updating the EM is and capacity orig > > of the system in this case. Similarly, we rebuild sched_domain with a > > cpu hotplug. scaling_max_freq interface should not be used to do any > > kind of dynamic scaling. > > I tend to agree, but the EM capacity would be only used in part of EAS > code. The whole fair.c view to the capacity_of() (RT + DL + irq + > thermal_pressure) would be still wrong in other parts, e.g. > select_idle_sibling() and load balance. > > When we get this powerhint we might be already in overutilied state > so EAS is disabled. IMO other mechanisms in the task scheduler > should be also aware of that capacity reduction.
That's why I also mentioned the capacity_orig
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