linux-kernel - Re: [PATCH] sched/fair: Introduce fits

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Date:   Wed, 17 Jul 2019 16:59:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH] sched/fair: Introduce fits_capacity()

On Wed, Jul 17, 2019 at 04:03:56PM +0530, Viresh Kumar wrote:
> On 04-06-19, 12:31, Viresh Kumar wrote:
> > The same formula to check utilization against capacity (after
> > considering capacity_margin) is already used at 5 different locations.
> > 
> > This patch creates a new macro, fits_capacity(), which can be used from
> > all these locations without exposing the details of it and hence
> > simplify code.
> > 
> > All the 5 code locations are updated as well to use it..
> > 
> > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> > ---
> >  kernel/sched/fair.c | 14 +++++++-------
> >  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> @Peter: Do you suggest any modifications to this patch? Do I need to
> resend it ?

Ah, I've picked it up with a few (small) edits.

Thanks!

---
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -96,12 +96,12 @@ int __weak arch_asym_cpu_priority(int cp
 }
 
 /*
- * The margin used when comparing utilization with CPU capacity:
- * util * margin < capacity * 1024
+ * The margin used when comparing utilization with CPU capacity.
  *
  * (default: ~20%)
  */
-static unsigned int capacity_margin			= 1280;
+#define fits_capacity(cap, max)	((cap) * 1280 < (max) * 1024)
+
 #endif
 
 #ifdef CONFIG_CFS_BANDWIDTH
@@ -3754,7 +3754,7 @@ util_est_dequeue(struct cfs_rq *cfs_rq,
 
 static inline int task_fits_capacity(struct task_struct *p, long capacity)
 {
-	return capacity * 1024 > task_util_est(p) * capacity_margin;
+	return fits_capacity(task_util_est(p), capacity);
 }
 
 static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
@@ -5181,7 +5181,7 @@ static inline unsigned long cpu_util(int
 
 static inline bool cpu_overutilized(int cpu)
 {
-	return (capacity_of(cpu) * 1024) < (cpu_util(cpu) * capacity_margin);
+	return !fits_capacity(cpu_util(cpu), capacity_of(cpu));
 }
 
 static inline void update_overutilized_status(struct rq *rq)
@@ -6402,7 +6402,7 @@ static int find_energy_efficient_cpu(str
 			/* Skip CPUs that will be overutilized. */
 			util = cpu_util_next(cpu, p, cpu);
 			cpu_cap = capacity_of(cpu);
-			if (cpu_cap * 1024 < util * capacity_margin)
+			if (!fits_capacity(util, cpu_cap))
 				continue;
 
 			/* Always use prev_cpu as a candidate. */
@@ -7957,8 +7957,7 @@ group_is_overloaded(struct lb_env *env,
 static inline bool
 group_smaller_min_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
 {
-	return sg->sgc->min_capacity * capacity_margin <
-						ref->sgc->min_capacity * 1024;
+	return fits_capacity(sg->sgc->min_capacity, ref->sgc->min_capacity);
 }
 
 /*
@@ -7968,8 +7967,7 @@ group_smaller_min_cpu_capacity(struct sc
 static inline bool
 group_smaller_max_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
 {
-	return sg->sgc->max_capacity * capacity_margin <
-						ref->sgc->max_capacity * 1024;
+	return fits_capacity(sg->sgc->max_capacity, ref->sgc->max_capacity);
 }
 
 static inline enum