From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
To:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>
Cc:     Vincent Guittot <vincent.guittot@linaro.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <valentin.schneider@arm.com>,
        linux-kernel@vger.kernel.org
Subject: [PATCH] sched/fair: Replace CFS internal cpu_util() with cpu_util_cfs()
Date:   Fri, 12 Nov 2021 15:13:49 +0100
Message-Id: <20211112141349.155713-1-dietmar.eggemann@arm.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

cpu_util_cfs() was created by commit d4edd662ac16 ("sched/cpufreq: Use
the DEADLINE utilization signal") to enable the access to CPU
utilization from the Schedutil CPUfreq governor.

Commit a07630b8b2c1 ("sched/cpufreq/schedutil: Use util_est for OPP
selection") added util_est support later.

The only thing cpu_util() is doing on top of what cpu_util_cfs() already
does is to clamp the return value to the [0..capacity_orig] capacity
range of the CPU. Integrating this into cpu_util_cfs() is not harming
the existing users (Schedutil and CPUfreq cooling (latter via
sched_cpu_util() wrapper)).

Remove cpu_util().

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
---

I deliberately got rid of the comment on top of cpu_util(). It's from
the early days of using PELT utilization, it describes CPU utilization
behaviour before PELT time-scaling and talks about current capacity
which we don't maintain. 

 kernel/sched/fair.c  | 65 ++++----------------------------------------
 kernel/sched/sched.h |  2 +-
 2 files changed, 6 insertions(+), 61 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 13950beb01a2..7a815b10c0c3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1502,7 +1502,6 @@ struct task_numa_env {
 
 static unsigned long cpu_load(struct rq *rq);
 static unsigned long cpu_runnable(struct rq *rq);
-static unsigned long cpu_util(int cpu);
 static inline long adjust_numa_imbalance(int imbalance,
 					int dst_running, int dst_weight);
 
@@ -1569,7 +1568,7 @@ static void update_numa_stats(struct task_numa_env *env,
 
 		ns->load += cpu_load(rq);
 		ns->runnable += cpu_runnable(rq);
-		ns->util += cpu_util(cpu);
+		ns->util += cpu_util_cfs(rq);
 		ns->nr_running += rq->cfs.h_nr_running;
 		ns->compute_capacity += capacity_of(cpu);
 
@@ -5509,11 +5508,9 @@ static inline void hrtick_update(struct rq *rq)
 #endif
 
 #ifdef CONFIG_SMP
-static inline unsigned long cpu_util(int cpu);
-
 static inline bool cpu_overutilized(int cpu)
 {
-	return !fits_capacity(cpu_util(cpu), capacity_of(cpu));
+	return !fits_capacity(cpu_util_cfs(cpu_rq(cpu)), capacity_of(cpu));
 }
 
 static inline void update_overutilized_status(struct rq *rq)
@@ -6456,58 +6453,6 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 	return target;
 }
 
-/**
- * cpu_util - Estimates the amount of capacity of a CPU used by CFS tasks.
- * @cpu: the CPU to get the utilization of
- *
- * The unit of the return value must be the one of capacity so we can compare
- * the utilization with the capacity of the CPU that is available for CFS task
- * (ie cpu_capacity).
- *
- * cfs_rq.avg.util_avg is the sum of running time of runnable tasks plus the
- * recent utilization of currently non-runnable tasks on a CPU. It represents
- * the amount of utilization of a CPU in the range [0..capacity_orig] where
- * capacity_orig is the cpu_capacity available at the highest frequency
- * (arch_scale_freq_capacity()).
- * The utilization of a CPU converges towards a sum equal to or less than the
- * current capacity (capacity_curr <= capacity_orig) of the CPU because it is
- * the running time on this CPU scaled by capacity_curr.
- *
- * The estimated utilization of a CPU is defined to be the maximum between its
- * cfs_rq.avg.util_avg and the sum of the estimated utilization of the tasks
- * currently RUNNABLE on that CPU.
- * This allows to properly represent the expected utilization of a CPU which
- * has just got a big task running since a long sleep period. At the same time
- * however it preserves the benefits of the "blocked utilization" in
- * describing the potential for other tasks waking up on the same CPU.
- *
- * Nevertheless, cfs_rq.avg.util_avg can be higher than capacity_curr or even
- * higher than capacity_orig because of unfortunate rounding in
- * cfs.avg.util_avg or just after migrating tasks and new task wakeups until
- * the average stabilizes with the new running time. We need to check that the
- * utilization stays within the range of [0..capacity_orig] and cap it if
- * necessary. Without utilization capping, a group could be seen as overloaded
- * (CPU0 utilization at 121% + CPU1 utilization at 80%) whereas CPU1 has 20% of
- * available capacity. We allow utilization to overshoot capacity_curr (but not
- * capacity_orig) as it useful for predicting the capacity required after task
- * migrations (scheduler-driven DVFS).
- *
- * Return: the (estimated) utilization for the specified CPU
- */
-static inline unsigned long cpu_util(int cpu)
-{
-	struct cfs_rq *cfs_rq;
-	unsigned int util;
-
-	cfs_rq = &cpu_rq(cpu)->cfs;
-	util = READ_ONCE(cfs_rq->avg.util_avg);
-
-	if (sched_feat(UTIL_EST))
-		util = max(util, READ_ONCE(cfs_rq->avg.util_est.enqueued));
-
-	return min_t(unsigned long, util, capacity_orig_of(cpu));
-}
-
 /*
  * cpu_util_without: compute cpu utilization without any contributions from *p
  * @cpu: the CPU which utilization is requested
@@ -6528,7 +6473,7 @@ static unsigned long cpu_util_without(int cpu, struct task_struct *p)
 
 	/* Task has no contribution or is new */
 	if (cpu != task_cpu(p) || !READ_ONCE(p->se.avg.last_update_time))
-		return cpu_util(cpu);
+		return cpu_util_cfs(cpu_rq(cpu));
 
 	cfs_rq = &cpu_rq(cpu)->cfs;
 	util = READ_ONCE(cfs_rq->avg.util_avg);
@@ -8681,7 +8626,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 		struct rq *rq = cpu_rq(i);
 
 		sgs->group_load += cpu_load(rq);
-		sgs->group_util += cpu_util(i);
+		sgs->group_util += cpu_util_cfs(rq);
 		sgs->group_runnable += cpu_runnable(rq);
 		sgs->sum_h_nr_running += rq->cfs.h_nr_running;
 
@@ -9699,7 +9644,7 @@ static struct rq *find_busiest_queue(struct lb_env *env,
 			break;
 
 		case migrate_util:
-			util = cpu_util(cpu_of(rq));
+			util = cpu_util_cfs(rq);
 
 			/*
 			 * Don't try to pull utilization from a CPU with one
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f0b249ec581d..d49eda251049 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2951,7 +2951,7 @@ static inline unsigned long cpu_util_cfs(struct rq *rq)
 			     READ_ONCE(rq->cfs.avg.util_est.enqueued));
 	}
 
-	return util;
+	return min(util, capacity_orig_of(cpu_of(rq)));
 }
 
 static inline unsigned long cpu_util_rt(struct rq *rq)
-- 
2.25.1