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Message-ID: <20230204184231.zx6oo52r5q2nvij7@airbuntu>
Date: Sat, 4 Feb 2023 18:42:31 +0000
From: Qais Yousef <qyousef@...alina.io>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: mingo@...nel.org, peterz@...radead.org, dietmar.eggemann@....com,
rafael@...nel.org, viresh.kumar@...aro.org, vschneid@...hat.com,
linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
kajetan.puchalski@....com, lukasz.luba@....com, wvw@...gle.com,
xuewen.yan94@...il.com, han.lin@...iatek.com,
Jonathan.JMChen@...iatek.com
Subject: Re: [PATCH 2/2 v5] sched/fair: Remove capacity inversion detection
On 02/01/23 15:36, Vincent Guittot wrote:
> Remove the capacity inversion detection which is now handled by
> util_fits_cpu() returning -1 when we need to continue to look for a
> potential CPU with better performance.
>
> This ends up almost reverting patches below except for some comments:
nit: I think this comment must be removed/reworeded though
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 691a2f9c4efa..c6c8e7f52935 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4476,10 +4476,6 @@ static inline int util_fits_cpu(unsigned long util,
*
* For uclamp_max, we can tolerate a drop in performance level as the
* goal is to cap the task. So it's okay if it's getting less.
- *
- * In case of capacity inversion, which is not handled yet, we should
- * honour the inverted capacity for both uclamp_min and uclamp_max all
- * the time.
*/
capacity_orig = capacity_orig_of(cpu);
capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);
> commit da07d2f9c153 ("sched/fair: Fixes for capacity inversion detection")
> commit aa69c36f31aa ("sched/fair: Consider capacity inversion in util_fits_cpu()")
> commit 44c7b80bffc3 ("sched/fair: Detect capacity inversion")
>
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
Apart from that, LGTM.
Reviewed-by: Qais Yousef <qyousef@...alina.io>
Thanks!
--
Qais Yousef
> ---
> kernel/sched/fair.c | 84 +++-----------------------------------------
> kernel/sched/sched.h | 19 ----------
> 2 files changed, 5 insertions(+), 98 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 074742f107c0..c6c8e7f52935 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4476,17 +4476,9 @@ static inline int util_fits_cpu(unsigned long util,
> *
> * For uclamp_max, we can tolerate a drop in performance level as the
> * goal is to cap the task. So it's okay if it's getting less.
> - *
> - * In case of capacity inversion we should honour the inverted capacity
> - * for both uclamp_min and uclamp_max all the time.
> */
> - capacity_orig = cpu_in_capacity_inversion(cpu);
> - if (capacity_orig) {
> - capacity_orig_thermal = capacity_orig;
> - } else {
> - capacity_orig = capacity_orig_of(cpu);
> - capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);
> - }
> + capacity_orig = capacity_orig_of(cpu);
> + capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);
>
> /*
> * We want to force a task to fit a cpu as implied by uclamp_max.
> @@ -9027,82 +9019,16 @@ static unsigned long scale_rt_capacity(int cpu)
>
> static void update_cpu_capacity(struct sched_domain *sd, int cpu)
> {
> - unsigned long capacity_orig = arch_scale_cpu_capacity(cpu);
> unsigned long capacity = scale_rt_capacity(cpu);
> struct sched_group *sdg = sd->groups;
> - struct rq *rq = cpu_rq(cpu);
>
> - rq->cpu_capacity_orig = capacity_orig;
> + cpu_rq(cpu)->cpu_capacity_orig = arch_scale_cpu_capacity(cpu);
>
> if (!capacity)
> capacity = 1;
>
> - rq->cpu_capacity = capacity;
> -
> - /*
> - * Detect if the performance domain is in capacity inversion state.
> - *
> - * Capacity inversion happens when another perf domain with equal or
> - * lower capacity_orig_of() ends up having higher capacity than this
> - * domain after subtracting thermal pressure.
> - *
> - * We only take into account thermal pressure in this detection as it's
> - * the only metric that actually results in *real* reduction of
> - * capacity due to performance points (OPPs) being dropped/become
> - * unreachable due to thermal throttling.
> - *
> - * We assume:
> - * * That all cpus in a perf domain have the same capacity_orig
> - * (same uArch).
> - * * Thermal pressure will impact all cpus in this perf domain
> - * equally.
> - */
> - if (sched_energy_enabled()) {
> - unsigned long inv_cap = capacity_orig - thermal_load_avg(rq);
> - struct perf_domain *pd;
> -
> - rcu_read_lock();
> -
> - pd = rcu_dereference(rq->rd->pd);
> - rq->cpu_capacity_inverted = 0;
> -
> - for (; pd; pd = pd->next) {
> - struct cpumask *pd_span = perf_domain_span(pd);
> - unsigned long pd_cap_orig, pd_cap;
> -
> - /* We can't be inverted against our own pd */
> - if (cpumask_test_cpu(cpu_of(rq), pd_span))
> - continue;
> -
> - cpu = cpumask_any(pd_span);
> - pd_cap_orig = arch_scale_cpu_capacity(cpu);
> -
> - if (capacity_orig < pd_cap_orig)
> - continue;
> -
> - /*
> - * handle the case of multiple perf domains have the
> - * same capacity_orig but one of them is under higher
> - * thermal pressure. We record it as capacity
> - * inversion.
> - */
> - if (capacity_orig == pd_cap_orig) {
> - pd_cap = pd_cap_orig - thermal_load_avg(cpu_rq(cpu));
> -
> - if (pd_cap > inv_cap) {
> - rq->cpu_capacity_inverted = inv_cap;
> - break;
> - }
> - } else if (pd_cap_orig > inv_cap) {
> - rq->cpu_capacity_inverted = inv_cap;
> - break;
> - }
> - }
> -
> - rcu_read_unlock();
> - }
> -
> - trace_sched_cpu_capacity_tp(rq);
> + cpu_rq(cpu)->cpu_capacity = capacity;
> + trace_sched_cpu_capacity_tp(cpu_rq(cpu));
>
> sdg->sgc->capacity = capacity;
> sdg->sgc->min_capacity = capacity;
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 1072502976df..3e8df6d31c1e 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1044,7 +1044,6 @@ struct rq {
>
> unsigned long cpu_capacity;
> unsigned long cpu_capacity_orig;
> - unsigned long cpu_capacity_inverted;
>
> struct balance_callback *balance_callback;
>
> @@ -2899,24 +2898,6 @@ static inline unsigned long capacity_orig_of(int cpu)
> return cpu_rq(cpu)->cpu_capacity_orig;
> }
>
> -/*
> - * Returns inverted capacity if the CPU is in capacity inversion state.
> - * 0 otherwise.
> - *
> - * Capacity inversion detection only considers thermal impact where actual
> - * performance points (OPPs) gets dropped.
> - *
> - * Capacity inversion state happens when another performance domain that has
> - * equal or lower capacity_orig_of() becomes effectively larger than the perf
> - * domain this CPU belongs to due to thermal pressure throttling it hard.
> - *
> - * See comment in update_cpu_capacity().
> - */
> -static inline unsigned long cpu_in_capacity_inversion(int cpu)
> -{
> - return cpu_rq(cpu)->cpu_capacity_inverted;
> -}
> -
> /**
> * enum cpu_util_type - CPU utilization type
> * @FREQUENCY_UTIL: Utilization used to select frequency
> --
> 2.34.1
>
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