| Message ID | 480f2140-ea59-4e1d-a68d-18cbcec10941@arm.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | cpufreq/schedutil: Only bind threads if needed | expand |
Hi, On 12/09/24 17:01, Christian Loehle wrote: > On 9/12/24 16:41, Rafael J. Wysocki wrote: > > On Thu, Sep 12, 2024 at 3:53 PM Christian Loehle ... > >> diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c > >> index c62acf509b74..7d4a4edfcfb9 100644 > >> --- a/kernel/sched/syscalls.c > >> +++ b/kernel/sched/syscalls.c > >> @@ -1159,6 +1159,9 @@ int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask) > >> if (!task_has_dl_policy(p) || !dl_bandwidth_enabled()) > >> return 0; > >> > >> + if (dl_entity_is_special(&p->dl)) > >> + return 0; > >> + > > > > Care to explain this particular piece? > > Looks suspicious but the truncated comment below explains it: > /* > * Since bandwidth control happens on root_domain basis, > * if admission test is enabled, we only admit -deadline > * tasks allowed to run on all the CPUs in the task's > * root_domain. > */ > So that would only allow setting it to all CPUs for the relevant > platforms unfortunately. > > That should be fine though since the sugov task is pretty much > a dummy in terms of bandwidth / admission control internally, so > no harm done to not enforce this when userspace wants to set > affinities. > ...Unless Juri disagrees. Nope, I agree. :) Wonder if we should put a comment along the lines of what you said above right above the new conditions (so that people will not need to wonder about it in the future). But not a strict requirement for me. Thanks! (and apologies for the delay in replying) Juri
On 9/25/24 09:14, Juri Lelli wrote: > Hi, > > On 12/09/24 17:01, Christian Loehle wrote: >> On 9/12/24 16:41, Rafael J. Wysocki wrote: >>> On Thu, Sep 12, 2024 at 3:53 PM Christian Loehle > > ... > >>>> diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c >>>> index c62acf509b74..7d4a4edfcfb9 100644 >>>> --- a/kernel/sched/syscalls.c >>>> +++ b/kernel/sched/syscalls.c >>>> @@ -1159,6 +1159,9 @@ int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask) >>>> if (!task_has_dl_policy(p) || !dl_bandwidth_enabled()) >>>> return 0; >>>> >>>> + if (dl_entity_is_special(&p->dl)) >>>> + return 0; >>>> + >>> >>> Care to explain this particular piece? >> >> Looks suspicious but the truncated comment below explains it: >> /* >> * Since bandwidth control happens on root_domain basis, >> * if admission test is enabled, we only admit -deadline >> * tasks allowed to run on all the CPUs in the task's >> * root_domain. >> */ >> So that would only allow setting it to all CPUs for the relevant >> platforms unfortunately. >> >> That should be fine though since the sugov task is pretty much >> a dummy in terms of bandwidth / admission control internally, so >> no harm done to not enforce this when userspace wants to set >> affinities. >> ...Unless Juri disagrees. > > Nope, I agree. :) > > Wonder if we should put a comment along the lines of what you said above > right above the new conditions (so that people will not need to wonder > about it in the future). But not a strict requirement for me. > > Thanks! (and apologies for the delay in replying) > Juri Thank you Juri for taking a look. I agree with the comment, will do a v2. Regards, Christian
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index 43111a515a28..466fb79e0b81 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -683,7 +683,11 @@ static int sugov_kthread_create(struct sugov_policy *sg_policy) } sg_policy->thread = thread; - kthread_bind_mask(thread, policy->related_cpus); + if (policy->dvfs_possible_from_any_cpu) + set_cpus_allowed_ptr(thread, policy->related_cpus); + else + kthread_bind_mask(thread, policy->related_cpus); + init_irq_work(&sg_policy->irq_work, sugov_irq_work); mutex_init(&sg_policy->work_lock); diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c index c62acf509b74..7d4a4edfcfb9 100644 --- a/kernel/sched/syscalls.c +++ b/kernel/sched/syscalls.c @@ -1159,6 +1159,9 @@ int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask) if (!task_has_dl_policy(p) || !dl_bandwidth_enabled()) return 0; + if (dl_entity_is_special(&p->dl)) + return 0; + /* * Since bandwidth control happens on root_domain basis, * if admission test is enabled, we only admit -deadline
Remove the unconditional binding of sugov kthreads to the affected CPUs if the cpufreq driver indicates that updates can happen from any CPU. This allows userspace to set affinities to either save power (waking up bigger CPUs on HMP can be expensive) or increasing performance (by letting the utilized CPUs run without preemption of the sugov kthread). Without this patch the behavior of sugov threads will basically be a boot-time dice roll on which CPU of the PD has to handle all the cpufreq updates. With the recent decreases of update filtering these two basic problems become more and more apparent: 1. The wake_cpu might be idle and we are waking it up from another CPU just for the cpufreq update. Apart from wasting power, the exit latency of it's idle state might be longer than the sugov threads running time, essentially delaying the cpufreq update unnecessarily. 2. We are preempting either the requesting or another busy CPU of the PD, while the update could be done from a CPU that we deem less important and pay the price of an IPI and two context-switches. The change is essentially not setting PF_NO_SETAFFINITY on dvfs_possible_from_any_cpu, no behavior change if userspace doesn't touch affinities. Signed-off-by: Christian Loehle <christian.loehle@arm.com> --- kernel/sched/cpufreq_schedutil.c | 6 +++++- kernel/sched/syscalls.c | 3 +++ 2 files changed, 8 insertions(+), 1 deletion(-)