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Subject[RFC PATCH v2 8/8] sched/deadline: make bandwidth enforcement scale-invariant
Date
From: Juri Lelli <juri.lelli@arm.com>

Apply frequency and cpu scale-invariance correction factor to bandwidth
enforcement (similar to what we already do to fair utilization tracking).

Each delta_exec gets scaled considering current frequency and maximum
cpu capacity; which means that the reservation runtime parameter (that
need to be specified profiling the task execution at max frequency on
biggest capacity core) gets thus scaled accordingly.

Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Luca Abeni <luca.abeni@santannapisa.it>
Cc: Claudio Scordino <claudio@evidence.eu.com>
---
kernel/sched/deadline.c | 26 ++++++++++++++++++++++----
kernel/sched/fair.c | 2 --
kernel/sched/sched.h | 2 ++
3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 40f12aab9250..741d2fe26f88 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1151,7 +1151,8 @@ static void update_curr_dl(struct rq *rq)
{
struct task_struct *curr = rq->curr;
struct sched_dl_entity *dl_se = &curr->dl;
- u64 delta_exec;
+ u64 delta_exec, scaled_delta_exec;
+ int cpu = cpu_of(rq);

if (!dl_task(curr) || !on_dl_rq(dl_se))
return;
@@ -1185,9 +1186,26 @@ static void update_curr_dl(struct rq *rq)
if (unlikely(dl_entity_is_special(dl_se)))
return;

- if (unlikely(dl_se->flags & SCHED_FLAG_RECLAIM))
- delta_exec = grub_reclaim(delta_exec, rq, &curr->dl);
- dl_se->runtime -= delta_exec;
+ /*
+ * For tasks that participate in GRUB, we implement GRUB-PA: the
+ * spare reclaimed bandwidth is used to clock down frequency.
+ *
+ * For the others, we still need to scale reservation parameters
+ * according to current frequency and CPU maximum capacity.
+ */
+ if (unlikely(dl_se->flags & SCHED_FLAG_RECLAIM)) {
+ scaled_delta_exec = grub_reclaim(delta_exec,
+ rq,
+ &curr->dl);
+ } else {
+ unsigned long scale_freq = arch_scale_freq_capacity(cpu);
+ unsigned long scale_cpu = arch_scale_cpu_capacity(NULL, cpu);
+
+ scaled_delta_exec = cap_scale(delta_exec, scale_freq);
+ scaled_delta_exec = cap_scale(scaled_delta_exec, scale_cpu);
+ }
+
+ dl_se->runtime -= scaled_delta_exec;

throttle:
if (dl_runtime_exceeded(dl_se) || dl_se->dl_yielded) {
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 535d9409f4af..5bc3273a5c1c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3091,8 +3091,6 @@ static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)
return c1 + c2 + c3;
}

-#define cap_scale(v, s) ((v)*(s) >> SCHED_CAPACITY_SHIFT)
-
/*
* Accumulate the three separate parts of the sum; d1 the remainder
* of the last (incomplete) period, d2 the span of full periods and d3
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0022c649fabb..6d9d55e764fa 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -156,6 +156,8 @@ static inline int task_has_dl_policy(struct task_struct *p)
return dl_policy(p->policy);
}

+#define cap_scale(v, s) ((v)*(s) >> SCHED_CAPACITY_SHIFT)
+
/*
* !! For sched_setattr_nocheck() (kernel) only !!
*
--
2.14.3
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