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Subject[PATCH 09/11] sched: use pelt for scale_rt_capacity()
Date
The utilization of the CPU by rt, dl and interrupts are now tracked with
PELT so we can use these metrics instead of rt_avg to evaluate the remaining
capacity available for cfs class.

scale_rt_capacity() behavior has been changed and now returns the remaining
capacity available for cfs instead of a scaling factor because rt, dl and
interrupt provide now absolute utilization value.

The same formula as schedutil is used:
irq util_avg + (1 - irq util_avg / max capacity ) * /Sum rq util_avg
but the implementation is different because it doesn't return the same value
and doesn't benefit of the same optimization

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/deadline.c | 2 --
kernel/sched/fair.c | 41 +++++++++++++++++++----------------------
kernel/sched/pelt.c | 2 +-
kernel/sched/rt.c | 2 --
4 files changed, 20 insertions(+), 27 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index f4de2698..68b8a9f 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1180,8 +1180,6 @@ static void update_curr_dl(struct rq *rq)
curr->se.exec_start = now;
cgroup_account_cputime(curr, delta_exec);

- sched_rt_avg_update(rq, delta_exec);
-
if (dl_entity_is_special(dl_se))
return;

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d2758e3..ce0dcbf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7550,39 +7550,36 @@ static inline int get_sd_load_idx(struct sched_domain *sd,
static unsigned long scale_rt_capacity(int cpu)
{
struct rq *rq = cpu_rq(cpu);
- u64 total, used, age_stamp, avg;
- s64 delta;
-
- /*
- * Since we're reading these variables without serialization make sure
- * we read them once before doing sanity checks on them.
- */
- age_stamp = READ_ONCE(rq->age_stamp);
- avg = READ_ONCE(rq->rt_avg);
- delta = __rq_clock_broken(rq) - age_stamp;
+ unsigned long max = arch_scale_cpu_capacity(NULL, cpu);
+ unsigned long used, irq, free;

- if (unlikely(delta < 0))
- delta = 0;
+#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
+ irq = READ_ONCE(rq->avg_irq.util_avg);

- total = sched_avg_period() + delta;
+ if (unlikely(irq >= max))
+ return 1;
+#endif

- used = div_u64(avg, total);
+ used = READ_ONCE(rq->avg_rt.util_avg);
+ used += READ_ONCE(rq->avg_dl.util_avg);

- if (likely(used < SCHED_CAPACITY_SCALE))
- return SCHED_CAPACITY_SCALE - used;
+ if (unlikely(used >= max))
+ return 1;

- return 1;
+ free = max - used;
+#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
+ free *= (max - irq);
+ free /= max;
+#endif
+ return free;
}

static void update_cpu_capacity(struct sched_domain *sd, int cpu)
{
- unsigned long capacity = arch_scale_cpu_capacity(sd, cpu);
+ unsigned long capacity = scale_rt_capacity(cpu);
struct sched_group *sdg = sd->groups;

- cpu_rq(cpu)->cpu_capacity_orig = capacity;
-
- capacity *= scale_rt_capacity(cpu);
- capacity >>= SCHED_CAPACITY_SHIFT;
+ cpu_rq(cpu)->cpu_capacity_orig = arch_scale_cpu_capacity(sd, cpu);

if (!capacity)
capacity = 1;
diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
index ead6d8b..35475c0 100644
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -237,7 +237,7 @@ ___update_load_avg(struct sched_avg *sa, unsigned long load, unsigned long runna
*/
sa->load_avg = div_u64(load * sa->load_sum, divider);
sa->runnable_load_avg = div_u64(runnable * sa->runnable_load_sum, divider);
- sa->util_avg = sa->util_sum / divider;
+ WRITE_ONCE(sa->util_avg, sa->util_sum / divider);
}

/*
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 0e3e57a..2a881bd 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -970,8 +970,6 @@ static void update_curr_rt(struct rq *rq)
curr->se.exec_start = now;
cgroup_account_cputime(curr, delta_exec);

- sched_rt_avg_update(rq, delta_exec);
-
if (!rt_bandwidth_enabled())
return;

--
2.7.4
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