Change CFS into a virtual deadline scheduler.
By flattening the grouping hierarchy into a single level we now end up with
tasks that have varying latency requirements. Tasks from group A might have a
larger latency period than those from group B as the period depends on the
number of runnable tasks within a group.
The current scheduling criteria does not take that into account - it assumes a
single latency period. In order to accommodate these varying latencies in the
scheduling decision, move to EDF [*] scheduling. We treat the tasks need + its
latency period as the deadline it has to meet. This includes the latency into
the scheduling decision.
[*] - EDF is correct up until load 1, after that it is not a closed system so
improvement is possible here. It is usable because the system strives to
generate the load 1 situation.
Signed-off-by: Peter Zijlstra <[EMAIL PROTECTED]>
---
include/linux/sched.h | 1 +
kernel/sched_fair.c | 6 +++++-
2 files changed, 6 insertions(+), 1 deletion(-)
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -925,6 +925,7 @@ struct sched_entity {
u64 exec_start;
u64 sum_exec_runtime;
u64 vruntime;
+ u64 vperiod;
u64 prev_sum_exec_runtime;
#ifdef CONFIG_SCHEDSTATS
Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -220,9 +220,11 @@ static inline u64 min_vruntime(u64 min_v
static inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
- return se->vruntime - cfs_rq->min_vruntime;
+ return se->vruntime + se->vperiod - cfs_rq->min_vruntime;
}
+static u64 sched_vslice_add(struct cfs_rq *cfs_rq, struct sched_entity *se);
+
/*
* Enqueue an entity into the rb-tree:
*/
@@ -240,6 +242,8 @@ static void __enqueue_entity(struct cfs_
if (se == cfs_rq->curr)
return;
+ se->vperiod = sched_vslice_add(cfs_rq, se);
+
cfs_rq = &rq_of(cfs_rq)->cfs;
link = &cfs_rq->tasks_timeline.rb_node;
--
--
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