linux-kernel - [PATCH] CFS: Add hierarchical tree-based penalty.

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Message-Id: <20101012062552.4D7F2CE142@carpathia.dereferenced.org>
Date:	Tue, 12 Oct 2010 00:32:02 -0500
From:	William Pitcock <nenolod@...eferenced.org>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH] CFS: Add hierarchical tree-based penalty.

Inspired by the recent change to BFS by Con Kolivas, this patch causes
vruntime to be penalized based on parent depth from their root task
group.

I have, for the moment, decided to make it a default feature since the
design of CFS ensures that broken applications depending on task enqueue
behaviour behaving traditionally will continue to work.

My method for applying the penalty is different than that of BFS, it
divides the vruntime by the number of parents the process has.

Signed-off-by: William Pitcock <nenolod@...eferenced.org>
---
 include/linux/sched.h   |    2 ++
 kernel/sched.c          |    4 ++++
 kernel/sched_fair.c     |    7 +++++++
 kernel/sched_features.h |   12 ++++++++++++
 4 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1e2a6db..49fca7c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1494,6 +1494,8 @@ struct task_struct {
 		unsigned long memsw_bytes; /* uncharged mem+swap usage */
 	} memcg_batch;
 #endif
+
+	int parent_count;
 };
 
 /* Future-safe accessor for struct task_struct's cpus_allowed. */
diff --git a/kernel/sched.c b/kernel/sched.c
index dc85ceb..0e55350 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2621,6 +2621,10 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
 #endif
 
 	rq = task_rq_lock(p, &flags);
+
+	if (!(clone_flags & CLONE_THREAD))
+		p->parent_count++;
+
 	activate_task(rq, p, 0);
 	trace_sched_wakeup_new(p, 1);
 	check_preempt_curr(rq, p, WF_FORK);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index db3f674..3059fe0 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -737,6 +737,13 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
 	if (initial && sched_feat(START_DEBIT))
 		vruntime += sched_vslice(cfs_rq, se);
 
+	if (sched_feat(HIERARCHICAL_PENALTY)) {
+		struct task_struct *tsk = task_of(se);
+
+		if (tsk->parent_count > 1)
+			vruntime /= tsk->parent_count;
+	}
+
 	/* sleeps up to a single latency don't count. */
 	if (!initial) {
 		unsigned long thresh = sysctl_sched_latency;
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index 83c66e8..cf17f97 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -45,6 +45,18 @@ SCHED_FEAT(LAST_BUDDY, 1)
 SCHED_FEAT(CACHE_HOT_BUDDY, 1)
 
 /*
+ * Hierarchical tree-based penalty: penalize service deficit by
+ * an order of magnitude for each parent process in the process
+ * tree.  This has the natural effect of forcing preference towards
+ * processes that are not fork()-hungry, like make(1), which helps
+ * to preserve good latency.
+ *
+ * This also has the side effect of providing in a limited way,
+ * per-user CPU entitlement partitioning.
+ */
+SCHED_FEAT(HIERARCHICAL_PENALTY, 1)
+
+/*
  * Use arch dependent cpu power functions
  */
 SCHED_FEAT(ARCH_POWER, 0)
-- 
1.7.2.1

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