[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-Id: <1190756127.18744.23.camel@earth>
Date: Tue, 25 Sep 2007 23:35:27 +0200
From: Dmitry Adamushko <dmitry.adamushko@...il.com>
To: Ingo Molnar <mingo@...e.hu>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org
Subject: Re: [git] CFS-devel, latest code
humm... I think, it'd be safer to have something like the following
change in place.
The thing is that __pick_next_entity() must never be called when
first_fair(cfs_rq) == NULL. It wouldn't be a problem, should 'run_node'
be the very first field of 'struct sched_entity' (and it's the second).
The 'nr_running != 0' check is _not_ enough, due to the fact that
'current' is not within the tree. Generic paths are ok (e.g. schedule()
as put_prev_task() is called previously)... I'm more worried about e.g.
migration_call() -> CPU_DEAD_FROZEN -> migrate_dead_tasks()... if
'current' == rq->idle, no problems.. if it's one of the SCHED_NORMAL
tasks (or imagine, some other use-cases in the future -- i.e. we should
not make outer world dependent on internal details of sched_fair class)
-- it may be "Houston, we've got a problem" case.
it's +16 bytes to the ".text". Another variant is to make 'run_node' the
first data member of 'struct sched_entity' but an additional check (se !
= NULL) is still needed in pick_next_entity().
what do you think?
---
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index dae714a..33b2376 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -563,9 +563,12 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq)
{
- struct sched_entity *se = __pick_next_entity(cfs_rq);
-
- set_next_entity(cfs_rq, se);
+ struct sched_entity *se = NULL;
+
+ if (first_fair(cfs_rq)) {
+ se = __pick_next_entity(cfs_rq);
+ set_next_entity(cfs_rq, se);
+ }
return se;
}
---
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists