Add a few comments to place_entity().
Signed-off-by: Peter Zijlstra <[email protected]>
---
kernel/sched_fair.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -582,19 +582,26 @@ place_entity(struct cfs_rq *cfs_rq, stru
} else if (sched_feat(APPROX_AVG) && cfs_rq->nr_running)
vruntime += sched_vslice(cfs_rq)/2;
+ /*
+ * The 'current' period is already promised to the current tasks,
+ * however the extra weight of the new task will slow them down a
+ * little, place the new task so that it fits in the slot that
+ * stays open at the end.
+ */
if (initial && sched_feat(START_DEBIT))
vruntime += sched_vslice_add(cfs_rq, se);
if (!initial) {
+ /* sleeps upto a single latency don't count. */
if (sched_feat(NEW_FAIR_SLEEPERS) && entity_is_task(se) &&
task_of(se)->policy != SCHED_BATCH)
vruntime -= sysctl_sched_latency;
- vruntime = max_t(s64, vruntime, se->vruntime);
+ /* ensure we never gain time by being placed backwards. */
+ vruntime = max_vruntime(se->vruntime, vruntime);
}
se->vruntime = vruntime;
-
}
static void
--
-
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