On Sat, Oct 06, 2018 at 06:22:11AM +0800, Peng Hao wrote: > find_lock_lowest_rq may or not releease rq lock when return > lowest_rq=NULL, but it is fuzzy. > If not releasing rq lock, it is unnecessary to re-call > pick_next_pushable_task. > When CONFIG_PREEMPT=n, not releasing rq lock and return > lowest_rq=null frequently happens in a simple test case: > Four different rt priority tasks run on limited two cpus. > Thanks for Steven Rostedt's advice.
Can we please write a more coherent Changelog, the above is very hard to read. Maybe something along the lines of: Subject: sched/rt: Reduce push_rt_task() retries Improve push_rt_task() by propagating the double_lock_balance() usage from find_lock_lowest_rq(), thereby reducing the number of cases where we have to assume rq->lock was dropped. > Signed-off-by: Peng Hao <[email protected]> > --- > kernel/sched/rt.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index 2e2955a..be0fc43 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1754,7 +1754,7 @@ static struct rq *find_lock_lowest_rq(struct > task_struct *task, struct rq *rq) > !task_on_rq_queued(task))) { > > double_unlock_balance(rq, lowest_rq); > - lowest_rq = NULL; > + lowest_rq = RETRY_TASK; > break; > } > } I'm confused.. should not: /* try again */ double_unlock_balance(rq, lowest_rq); lowest_rq = NULL; also return RETRY_TASK? That also is in the double_lock_balance() path and will this have had rq->lock() released.
