0001-Prevent-CFS-from-ignoring-boost-requests-from-KVM.patch

From a3c64f59e6fdc0975e480eced26144a6d0bc7182 Mon Sep 17 00:00:00 2001
From: Kenta Ishiguro <kentaishiguro@sslab.ics.keio.ac.jp>
Date: Wed, 14 Jul 2021 01:52:13 +0900
Subject: [PATCH 1/2] Prevent CFS from ignoring boost requests from KVM

This commit increases the vruntime of yielded vCPU to boost a vCPU
instead of the yielded vCPU when two vCPUs are in the same VM. This
change avoids the situation where scheduling the boosted vCPU is too
unfair.
---
 kernel/sched/fair.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c1217bfe5e81..a12c802e2322 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6878,10 +6878,26 @@ static void yield_task_fair(struct rq *rq)
 	set_skip_buddy(se);
 }
 
+static void deboost_yield_task_vruntime(struct sched_entity *next_se, struct sched_entity *yield_se)
+{
+	if (wakeup_preempt_entity(next_se, yield_se) >= 1)
+		yield_se->vruntime = next_se->vruntime - wakeup_gran(next_se);
+}
+
+static void deboost_yield_task(struct sched_entity *next_se, struct sched_entity *yield_se)
+{
+	if (cfs_rq_of(yield_se) != cfs_rq_of(next_se))
+		return;
+	deboost_yield_task_vruntime(next_se, yield_se);
+}
+
 static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preempt)
 {
 	struct sched_entity *se = &p->se;
 
+	struct task_struct *curr;
+	struct sched_entity *yield_se;
+
 	/* throttled hierarchies are not runnable */
 	if (!se->on_rq || throttled_hierarchy(cfs_rq_of(se)))
 		return false;
@@ -6889,6 +6905,10 @@ static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preemp
 	/* Tell the scheduler that we'd really like pse to run next. */
 	set_next_buddy(se);
 
+	curr = rq->curr;
+	yield_se = &curr->se;
+	deboost_yield_task(se, yield_se);
+
 	yield_task_fair(rq);
 
 	return true;
-- 
2.20.1