On 01/24/2011 01:04 PM, Peter Zijlstra wrote:
diff --git a/kernel/sched.c b/kernel/sched.c
index dc91a4d..e4e57ff 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -327,7 +327,7 @@ struct cfs_rq {
* 'curr' points to currently running entity on this cfs_rq.
* It is set to NULL otherwise (i.e when none are currently running).
*/
- struct sched_entity *curr, *next, *last;
+ struct sched_entity *curr, *next, *last, *yield;
I'd prefer it be called: skip or somesuch..
I could do that. Do any of the other scheduler people have
a preference?
+static struct sched_entity *__pick_second_entity(struct cfs_rq *cfs_rq)
+{
+ struct rb_node *left = cfs_rq->rb_leftmost;
+ struct rb_node *second;
+
+ if (!left)
+ return NULL;
+
+ second = rb_next(left);
+
+ if (!second)
+ second = left;
+
+ return rb_entry(second, struct sched_entity, run_node);
+}
So this works because you only ever skip the leftmost, should we perhaps
write this as something like the below?
Well, pick_next_entity only ever *picks* the leftmost entity,
so there's no reason to skip others.
@@ -813,6 +840,9 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
if (cfs_rq->next == se)
__clear_buddies_next(se);
+
+ if (cfs_rq->yield == se)
+ __clear_buddies_yield(se);
}
The 3rd hierarchy iteration.. :/
Except it won't actually walk up the tree above the level
where the buddy actually points at the se. I suspect the
new code will do less tree walking than the old code.
+ /*
+ * Someone really wants this to run. If it's not unfair, run it.
+ */
+ if (cfs_rq->next&& wakeup_preempt_entity(cfs_rq->next, left)< 1)
+ se = cfs_rq->next;
+
clear_buddies(cfs_rq, se);
return se;
This seems to assume ->yield cannot be ->next nor ->last, but I'm not
quite sure that will actually be true.
On the contrary, I specifically want ->next to be able to
override ->yield, for the reason that the _tasks_ that
have ->next and ->yield set could be inside the same _group_.
What I am assuming is that ->yield and ->last are not the
same task. This is achieved by yield_task_fair calling
clear_buddies.
+/*
+ * sched_yield() is very simple
+ *
+ * The magic of dealing with the ->yield buddy is in pick_next_entity.
+ */
+static void yield_task_fair(struct rq *rq)
+{
+ struct task_struct *curr = rq->curr;
+ struct cfs_rq *cfs_rq = task_cfs_rq(curr);
+ struct sched_entity *se =&curr->se;
+
+ /*
+ * Are we the only task in the tree?
+ */
+ if (unlikely(rq->nr_running == 1))
+ return;
+
+ clear_buddies(cfs_rq, se);
+
+ if (curr->policy != SCHED_BATCH) {
+ update_rq_clock(rq);
+ /*
+ * Update run-time statistics of the 'current'.
+ */
+ update_curr(cfs_rq);
+ }
+
+ set_yield_buddy(se);
+}
You just lost sysctl_sched_compat_yield, someone might be upset (I
really can't be bothered much with people using sys_yield :-), but if
you're going down that road you want a hunk in kernel/sysctl.c as well I
think.
I lost sysctl_sched_compat_yield, because with my code
yield is no longer a noop.
I'd be glad to remove the sysctl.c bits if you want :)
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