A very minor improvement, but might it be better to check sched_rt_runtime(rt_rq)
before taking the rt_runtime_lock?
Signed-off-by: Dimitri Sivanich <[email protected]>
--
kernel/sched_rt.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
Index: linux/kernel/sched_rt.c
===================================================================
--- linux.orig/kernel/sched_rt.c 2008-10-22 16:10:03.000000000 -0500
+++ linux/kernel/sched_rt.c 2008-10-31 07:57:19.000000000 -0500
@@ -537,13 +537,13 @@ static void update_curr_rt(struct rq *rq
for_each_sched_rt_entity(rt_se) {
rt_rq = rt_rq_of_se(rt_se);
- spin_lock(&rt_rq->rt_runtime_lock);
if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
+ spin_lock(&rt_rq->rt_runtime_lock);
rt_rq->rt_time += delta_exec;
if (sched_rt_runtime_exceeded(rt_rq))
resched_task(curr);
+ spin_unlock(&rt_rq->rt_runtime_lock);
}
- spin_unlock(&rt_rq->rt_runtime_lock);
}
}
On Fri, Oct 31, 2008 at 6:03 AM, Dimitri Sivanich <[email protected]> wrote:
> A very minor improvement, but might it be better to check sched_rt_runtime(rt_rq)
> before taking the rt_runtime_lock?
Is it possible that the attribute sched_rt_runtime is checking could
change by the time it acquires the lock? If not, should be fine, I
think.
- Steven
On Fri, Oct 31, 2008 at 06:10:13AM -0700, Steven Noonan wrote:
> On Fri, Oct 31, 2008 at 6:03 AM, Dimitri Sivanich <[email protected]> wrote:
> > A very minor improvement, but might it be better to check sched_rt_runtime(rt_rq)
> > before taking the rt_runtime_lock?
>
> Is it possible that the attribute sched_rt_runtime is checking could
> change by the time it acquires the lock? If not, should be fine, I
> think.
>
Steve,
While it might be possible for it to change in that instant, I don't know if it matters.
If the runtime value should change to RUNTIME_INF in that instant, it will be caught in sched_rt_runtime_exceeded(). If it changed from RUNTIME_INF to a lower value, I doubt it would matter much, as at most one more rt_rq value wouldn't be checked. Either way some rt_rq values would have been checked during the loop and some would not.
On Fri, 2008-10-31 at 08:03 -0500, Dimitri Sivanich wrote:
> A very minor improvement, but might it be better to check sched_rt_runtime(rt_rq)
> before taking the rt_runtime_lock?
Yes, I think its ok to do so.
Like pointed out in the other thread, there are two races:
- sched_rt_runtime() going to RUNTIME_INF, and that will be handled
properly by sched_rt_runtime_exceeded()
- sched_rt_runtime() going to !RUNTIME_INF, and here we can miss an
accounting cycle, but I don't think that is something to worry too
much about.
Acked-by: Peter Zijlstra <[email protected]>
> Signed-off-by: Dimitri Sivanich <[email protected]>
>
> --
>
> kernel/sched_rt.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> Index: linux/kernel/sched_rt.c
> ===================================================================
> --- linux.orig/kernel/sched_rt.c 2008-10-22 16:10:03.000000000 -0500
> +++ linux/kernel/sched_rt.c 2008-10-31 07:57:19.000000000 -0500
> @@ -537,13 +537,13 @@ static void update_curr_rt(struct rq *rq
> for_each_sched_rt_entity(rt_se) {
> rt_rq = rt_rq_of_se(rt_se);
>
> - spin_lock(&rt_rq->rt_runtime_lock);
> if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
> + spin_lock(&rt_rq->rt_runtime_lock);
> rt_rq->rt_time += delta_exec;
> if (sched_rt_runtime_exceeded(rt_rq))
> resched_task(curr);
> + spin_unlock(&rt_rq->rt_runtime_lock);
> }
> - spin_unlock(&rt_rq->rt_runtime_lock);
> }
> }
>
* Peter Zijlstra <[email protected]> wrote:
> On Fri, 2008-10-31 at 08:03 -0500, Dimitri Sivanich wrote:
> > A very minor improvement, but might it be better to check sched_rt_runtime(rt_rq)
> > before taking the rt_runtime_lock?
>
> Yes, I think its ok to do so.
>
> Like pointed out in the other thread, there are two races:
>
> - sched_rt_runtime() going to RUNTIME_INF, and that will be handled
> properly by sched_rt_runtime_exceeded()
>
> - sched_rt_runtime() going to !RUNTIME_INF, and here we can miss an
> accounting cycle, but I don't think that is something to worry too
> much about.
>
> Acked-by: Peter Zijlstra <[email protected]>
applied to tip/sched/rt, thanks guys!
Ingo