On Sat, 6 Oct 2018 06:22:11 +0800 Peng Hao <[email protected]> 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. > > 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; > } > } > @@ -1830,7 +1830,9 @@ static int push_rt_task(struct rq *rq) > > /* find_lock_lowest_rq locks the rq if found */ > lowest_rq = find_lock_lowest_rq(next_task, rq); > - if (!lowest_rq) { > + if (!lowest_rq) > + goto out; > + if (lowest_rq == RETRY_TASK) { This probably makes no difference, and can be blown off as just a preference, but should this be: if (!lowest_rq) { goto out; } else if (lowest_rq == RETRY_TASK) { The logic is the same regardless, so it's really just a matter of taste. That said: Reviewed-by: Steven Rostedt (VMware) <[email protected]> -- Steve > struct task_struct *task; > /* > * find_lock_lowest_rq releases rq->lock
