linux-kernel - Re: [PATCH 2/7] sched/uclamp: Make task_fits_capacity() use util_fits

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Date:   Fri, 22 Jul 2022 10:19:13 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Qais Yousef <qais.yousef@....com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        linux-kernel@...r.kernel.org, Xuewen Yan <xuewen.yan94@...il.com>,
        Wei Wang <wvw@...gle.com>,
        Jonathan JMChen <Jonathan.JMChen@...iatek.com>,
        Hank <han.lin@...iatek.com>
Subject: Re: [PATCH 2/7] sched/uclamp: Make task_fits_capacity() use
 util_fits_cpu()

Le jeudi 21 juil. 2022 à 15:29:49 (+0100), Qais Yousef a écrit :
> On 07/12/22 11:48, Qais Yousef wrote:
> > On 07/11/22 15:09, Vincent Guittot wrote:
> > > On Wed, 29 Jun 2022 at 21:48, Qais Yousef <qais.yousef@....com> wrote:
> > 

[...]

> > > > @@ -9108,7 +9125,7 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
> > > >
> > > >         /* Check if task fits in the group */
> > > >         if (sd->flags & SD_ASYM_CPUCAPACITY &&
> > > > -           !task_fits_capacity(p, group->sgc->max_capacity)) {
> > > > +           !task_fits_cpu(p, group->sgc->max_capacity_cpu)) {
> > > 
> > > All the changes and added complexity above for this line. Can't you
> > > find another way ?
> > 
> > You're right, I might have got carried away trying to keep the logic the same.
> > 
> > Can we use group->asym_prefer_cpu or pick a cpu from group->sgc->cpumask
> > instead?
> > 
> > I'll dig more into it anyway and try to come up with simpler alternative.
> 
> Actually we can't.
> 
> I can keep the current {max,min}_capacity field and just add the new
> {max,min}_capacity_cpu and use them where needed. Should address your concerns
> this way? That was actually the first version of the code, but then it seemed
> redundant to keep both {max,min}_capacity and {max,min}_capacity_cpu.
> 
> OR
> 
> I can add a new function to search for max spare capacity cpu in the group.
> 
> Preference?
> 

Isn't the below enough and much simpler ?

[PATCH] sched/uclamp: Make task_fits_capacity() use util_fits_cpu()

So that the new uclamp rules in regard to migration margin and capacity
pressure are taken into account correctly.
---
 kernel/sched/fair.c  | 25 +++++++++++++++----------
 kernel/sched/sched.h |  9 +++++++++
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5eecae32a0f6..3e0c7cc490be 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4317,10 +4317,12 @@ static inline int util_fits_cpu(unsigned long util,
 	return fits;
 }

-static inline int task_fits_capacity(struct task_struct *p,
-				     unsigned long capacity)
+static inline int task_fits_cpu(struct task_struct *p, int cpu)
 {
-	return fits_capacity(uclamp_task_util(p), capacity);
+	unsigned long uclamp_min = uclamp_eff_value(p, UCLAMP_MIN);
+	unsigned long uclamp_max = uclamp_eff_value(p, UCLAMP_MAX);
+	unsigned long util = task_util_est(p);
+	return util_fits_cpu(util, uclamp_min, uclamp_max, cpu);
 }

 static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
@@ -4333,7 +4335,7 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
 		return;
 	}

-	if (task_fits_capacity(p, capacity_of(cpu_of(rq)))) {
+	if (task_fits_cpu(p, cpu_of(rq))) {
 		rq->misfit_task_load = 0;
 		return;
 	}
@@ -8104,7 +8106,7 @@ static int detach_tasks(struct lb_env *env)

 		case migrate_misfit:
 			/* This is not a misfit task */
-			if (task_fits_capacity(p, capacity_of(env->src_cpu)))
+			if (task_fits_cpu(p, env->src_cpu))
 				goto next;

 			env->imbalance = 0;
@@ -9085,6 +9087,10 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,

 	memset(sgs, 0, sizeof(*sgs));

+	/* Assume that task can't fit any CPU of the group */
+	if (sd->flags & SD_ASYM_CPUCAPACITY)
+		sgs->group_misfit_task_load = 0;
+
 	for_each_cpu(i, sched_group_span(group)) {
 		struct rq *rq = cpu_rq(i);
 		unsigned int local;
@@ -9104,12 +9110,11 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
 		if (!nr_running && idle_cpu_without(i, p))
 			sgs->idle_cpus++;

-	}
+		/* Check if task fits in the CPU */
+		if (sd->flags & SD_ASYM_CPUCAPACITY &&
+		    task_fits_cpu(p, i))
+			sgs->group_misfit_task_load = 0;

-	/* Check if task fits in the group */
-	if (sd->flags & SD_ASYM_CPUCAPACITY &&
-	    !task_fits_capacity(p, group->sgc->max_capacity)) {
-		sgs->group_misfit_task_load = 1;
 	}

 	sgs->group_capacity = group->sgc->capacity;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 02c970501295..3292ad2db4ac 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2988,6 +2988,15 @@ static inline bool uclamp_is_used(void)
 	return static_branch_likely(&sched_uclamp_used);
 }
 #else /* CONFIG_UCLAMP_TASK */
+static inline unsigned long uclamp_eff_value(struct task_struct *p,
+					     enum uclamp_id clamp_id)
+{
+	if (clamp_id == UCLAMP_MIN)
+		return 0;
+
+	return SCHED_CAPACITY_SCALE;
+}
+
 static inline
 unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
 				  struct task_struct *p)
--
2.17.1

> 
> Thanks!
> 
> --
> Qais Yousef