[RFC v4 4/6] sched/deadline: implement GRUB accounting

[Luca Abeni <luca.abeni@unitn.it>]

From: Luca Abeni <luca.abeni@unitn.it>

According to the GRUB (Greedy Reclaimation of Unused Bandwidth)
reclaiming algorithm, the runtime is not decreased as "dq = -dt",
but as "dq = -Uact dt" (where Uact is the per-runqueue active
utilization).
Hence, this commit modifies the runtime accounting rule in
update_curr_dl() to implement the GRUB rule.

Signed-off-by: Luca Abeni <luca.abeni@unitn.it>
---
 kernel/sched/deadline.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index c087c3d..361887b 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -764,6 +764,19 @@ int dl_runtime_exceeded(struct sched_dl_entity *dl_se)
 extern bool sched_rt_bandwidth_account(struct rt_rq *rt_rq);
 
 /*
+ * This function implements the GRUB accounting rule:
+ * according to the GRUB reclaiming algorithm, the runtime is
+ * not decreased as "dq = -dt", but as "dq = -Uact dt", where
+ * Uact is the (per-runqueue) active utilization.
+ * Since rq->dl.running_bw contains Uact * 2^20, the result
+ * has to be shifted right by 20.
+ */
+u64 grub_reclaim(u64 delta, struct rq *rq)
+{
+	return (delta * rq->dl.running_bw) >> 20;
+}
+
+/*
  * Update the current task's runtime statistics (provided it is still
  * a -deadline task and has not been removed from the dl_rq).
  */
@@ -805,6 +818,7 @@ static void update_curr_dl(struct rq *rq)
 
 	sched_rt_avg_update(rq, delta_exec);
 
+	delta_exec = grub_reclaim(delta_exec, rq);
 	dl_se->runtime -= delta_exec;
 
 throttle:
-- 
2.7.4