Messages in this thread | | | Date | Sun, 19 Oct 2008 09:29:58 +0400 | From | Cyrill Gorcunov <> | Subject | Re: CFS related question |
| |
[Peter Zijlstra - Sat, Oct 18, 2008 at 10:28:18PM +0200] | On Sun, 2008-10-19 at 00:03 +0400, Cyrill Gorcunov wrote: | > Hi Ingo, Peter, | > | > I just curious, look we have the following | > | > static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq) | > { | > struct sched_entity *se = NULL; | > | > if (first_fair(cfs_rq)) { | > se = __pick_next_entity(cfs_rq); | > se = pick_next(cfs_rq, se); | > set_next_entity(cfs_rq, se); | > } | > | > return se; | > } | > | > which I presume may return NULL so the following piece | > could fail | > | > static struct task_struct *pick_next_task_fair(struct rq *rq) | > { | > struct task_struct *p; | > struct cfs_rq *cfs_rq = &rq->cfs; | > struct sched_entity *se; | > | > if (unlikely(!cfs_rq->nr_running)) | > return NULL; | > | > do { | > --> se = pick_next_entity(cfs_rq); | > --> OOPs cfs_rq = group_cfs_rq(se); | > } while (cfs_rq); | > | > p = task_of(se); | > hrtick_start_fair(rq, p); | > | > return p; | > } | > | > Did I miss something? Or it comepletely can NOT happen? | | pick_next_entity() only returns NULL when !first_fair(), which is when ! | nr_running. | | So the initial !nr_running check in pick_next_task_fair() will catch | that. Further nested RQs will never have !nr_running because then they | get dequeued. | | |
Thanks Peter!
- Cyrill -
| |