Messages in this thread Patch in this message | | | Date | Tue, 16 Oct 2018 14:35:17 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3] sched/rt : return accurate release rq lock info |
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On Mon, Oct 15, 2018 at 11:42:20AM -0400, Steven Rostedt wrote: > On Mon, 15 Oct 2018 11:20:32 +0200 > Peter Zijlstra <peterz@infradead.org> wrote: > > > > 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. > > I thought the same thing at first, but this is in the loop path, where > it does everything again. But now looking closer, I think there's a bug > in the original code.
So I find that whole thing utterly confusing; what about we start with something like so?
--- kernel/sched/rt.c | 51 +++++++++++++++++++++++---------------------------- 1 file changed, 23 insertions(+), 28 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 2e2955a8cf8f..237c84c2b042 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1714,6 +1714,26 @@ static int find_lowest_rq(struct task_struct *task) return -1; } +static struct task_struct *first_pushable_task(struct rq *rq) +{ + struct task_struct *p; + + if (!has_pushable_tasks(rq)) + return NULL; + + p = plist_first_entry(&rq->rt.pushable_tasks, + struct task_struct, pushable_tasks); + + BUG_ON(rq->cpu != task_cpu(p)); + BUG_ON(task_current(rq, p)); + BUG_ON(p->nr_cpus_allowed <= 1); + + BUG_ON(!task_on_rq_queued(p)); + BUG_ON(!rt_task(p)); + + return p; +} + /* Will lock the rq it finds */ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) { @@ -1747,12 +1767,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) * migrated already or had its affinity changed. * Also make sure that it wasn't scheduled on its rq. */ - if (unlikely(task_rq(task) != rq || - !cpumask_test_cpu(lowest_rq->cpu, &task->cpus_allowed) || - task_running(rq, task) || - !rt_task(task) || - !task_on_rq_queued(task))) { - + if (first_pushable_task(rq) != task) double_unlock_balance(rq, lowest_rq); lowest_rq = NULL; break; @@ -1771,26 +1786,6 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) return lowest_rq; } -static struct task_struct *pick_next_pushable_task(struct rq *rq) -{ - struct task_struct *p; - - if (!has_pushable_tasks(rq)) - return NULL; - - p = plist_first_entry(&rq->rt.pushable_tasks, - struct task_struct, pushable_tasks); - - BUG_ON(rq->cpu != task_cpu(p)); - BUG_ON(task_current(rq, p)); - BUG_ON(p->nr_cpus_allowed <= 1); - - BUG_ON(!task_on_rq_queued(p)); - BUG_ON(!rt_task(p)); - - return p; -} - /* * If the current CPU has more than one RT task, see if the non * running task can migrate over to a CPU that is running a task @@ -1805,7 +1800,7 @@ static int push_rt_task(struct rq *rq) if (!rq->rt.overloaded) return 0; - next_task = pick_next_pushable_task(rq); + next_task = first_pushable_task(rq); if (!next_task) return 0; @@ -1840,7 +1835,7 @@ static int push_rt_task(struct rq *rq) * run-queue and is also still the next task eligible for * pushing. */ - task = pick_next_pushable_task(rq); + task = first_pushable_task(rq); if (task == next_task) { /* * The task hasn't migrated, and is still the next
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