* Re: [PATCH v2] sched/rt : return accurate release rq lock info
2018-10-02 20:17 [PATCH v2] sched/rt : return accurate release rq lock info Peng Hao
@ 2018-10-02 15:18 ` Steven Rostedt
0 siblings, 0 replies; 2+ messages in thread
From: Steven Rostedt @ 2018-10-02 15:18 UTC (permalink / raw)
To: Peng Hao; +Cc: mingo, peterz, linux-kernel
On Wed, 3 Oct 2018 04:17:22 +0800
Peng Hao <peng.hao2@zte.com.cn> wrote:
> find_lock_lowest_rq may or not releease rq lock, 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 frequently happens
> in a simple test case:
> Four different rt priority tasks run on limited two cpus.
>
> Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
> ---
> kernel/sched/rt.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 2e2955a..7c5382a 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1718,6 +1718,7 @@ static int find_lowest_rq(struct task_struct *task)
> static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
> {
> struct rq *lowest_rq = NULL;
> + bool release_lock = false;
> int tries;
> int cpu;
>
> @@ -1741,6 +1742,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
>
> /* if the prio of this runqueue changed, try again */
> if (double_lock_balance(rq, lowest_rq)) {
> + release_lock = true;
> /*
> * We had to unlock the run queue. In
> * the mean time, task could have
> @@ -1768,6 +1770,8 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
> lowest_rq = NULL;
> }
>
> + if (!lowest_rq && release_lock)
> + lowest_rq = RETRY_TASK;
> return lowest_rq;
> }
Instead of adding the above boolean variable, wouldn't this work just
as well?
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 2e2955a8cf8f..b363ef70412a 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 +1834,7 @@ 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) {
Not a biggy, but I would add here:
if (!lowest_rq)
goto out;
And then add the below. It just flows better.
-- Steve
> + if (lowest_rq == RETRY_TASK) {
> struct task_struct *task;
> /*
> * find_lock_lowest_rq releases rq->lock
> @@ -1863,6 +1867,8 @@ static int push_rt_task(struct rq *rq)
> goto retry;
> }
>
> + if (!lowest_rq)
> + goto out;
> deactivate_task(rq, next_task, 0);
> set_task_cpu(next_task, lowest_rq->cpu);
> activate_task(lowest_rq, next_task, 0);
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [PATCH v2] sched/rt : return accurate release rq lock info
@ 2018-10-02 20:17 Peng Hao
2018-10-02 15:18 ` Steven Rostedt
0 siblings, 1 reply; 2+ messages in thread
From: Peng Hao @ 2018-10-02 20:17 UTC (permalink / raw)
To: mingo, peterz; +Cc: linux-kernel, Peng Hao
find_lock_lowest_rq may or not releease rq lock, 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 frequently happens
in a simple test case:
Four different rt priority tasks run on limited two cpus.
Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
---
kernel/sched/rt.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 2e2955a..7c5382a 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1718,6 +1718,7 @@ static int find_lowest_rq(struct task_struct *task)
static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
{
struct rq *lowest_rq = NULL;
+ bool release_lock = false;
int tries;
int cpu;
@@ -1741,6 +1742,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
/* if the prio of this runqueue changed, try again */
if (double_lock_balance(rq, lowest_rq)) {
+ release_lock = true;
/*
* We had to unlock the run queue. In
* the mean time, task could have
@@ -1768,6 +1770,8 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
lowest_rq = NULL;
}
+ if (!lowest_rq && release_lock)
+ lowest_rq = RETRY_TASK;
return lowest_rq;
}
@@ -1830,7 +1834,7 @@ 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 == RETRY_TASK) {
struct task_struct *task;
/*
* find_lock_lowest_rq releases rq->lock
@@ -1863,6 +1867,8 @@ static int push_rt_task(struct rq *rq)
goto retry;
}
+ if (!lowest_rq)
+ goto out;
deactivate_task(rq, next_task, 0);
set_task_cpu(next_task, lowest_rq->cpu);
activate_task(lowest_rq, next_task, 0);
--
1.8.3.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
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