[RFC][PATCH] sched: deadline: Remove unnecessary goto label in pick_earliest_pushable_dl_task

[RFC][PATCH] sched: deadline: Remove unnecessary goto label in pick_earliest_pushable_dl_task

[John Stultz]

Commit 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
added an odd goto label that seems to be unnecssary, given its
called unconditionally from the bottom of a while loop and the
label is at the top.

Thus, clean it up and remove the label/goto.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Wanpeng Li <wanpeng.li@linux.intel.com>
Cc: Todd Kjos <tkjos@google.com>
Cc: kernel-team@android.com
Fixes: 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
Reported-by: Todd Kjos <tkjos@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
---
 kernel/sched/deadline.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index d9d5a702f1a61..566a05efa4e57 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2501,8 +2501,6 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
 		return NULL;
 
 	next_node = rb_first_cached(&rq->dl.pushable_dl_tasks_root);
-
-next_node:
 	if (next_node) {
 		p = __node_2_pdl(next_node);
 
@@ -2510,7 +2508,6 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
 			return p;
 
 		next_node = rb_next(next_node);
-		goto next_node;
 	}
 
 	return NULL;
-- 
2.47.0.338.g60cca15819-goog

Re: [RFC][PATCH] sched: deadline: Remove unnecessary goto label in pick_earliest_pushable_dl_task

[Christophe JAILLET]

Le 05/12/2024 à 22:16, John Stultz a écrit :
> Commit 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
> added an odd goto label that seems to be unnecssary, given its

s/unnecssary/unnecessary/

> called unconditionally from the bottom of a while loop and the
> label is at the top.

Except that it is not a while loop, but only an if.

Maybe, changing this if into a while would save a few lines of code and 
be more readable as-well.

CJ

> 
> Thus, clean it up and remove the label/goto.
> 
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Wanpeng Li <wanpeng.li@linux.intel.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: kernel-team@android.com
> Fixes: 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
> Reported-by: Todd Kjos <tkjos@google.com>
> Signed-off-by: John Stultz <jstultz@google.com>
> ---
>   kernel/sched/deadline.c | 3 ---
>   1 file changed, 3 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index d9d5a702f1a61..566a05efa4e57 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -2501,8 +2501,6 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
>   		return NULL;
>   
>   	next_node = rb_first_cached(&rq->dl.pushable_dl_tasks_root);
> -
> -next_node:
>   	if (next_node) {
>   		p = __node_2_pdl(next_node);
>   
> @@ -2510,7 +2508,6 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
>   			return p;
>   
>   		next_node = rb_next(next_node);
> -		goto next_node;
>   	}
>   
>   	return NULL;

Re: [RFC][PATCH] sched: deadline: Remove unnecessary goto label in pick_earliest_pushable_dl_task

[Christophe JAILLET]

Le 05/12/2024 à 22:16, John Stultz a écrit :
> Commit 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
> added an odd goto label that seems to be unnecssary, given its

s/unnecssary/unnecessary/

> called unconditionally from the bottom of a while loop and the
> label is at the top.

Except that it is not a while loop, but only an if.

Maybe, changing this if into a while would save a few lines of code and 
be more readable as-well.

CJ

> 
> Thus, clean it up and remove the label/goto.
> 
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Wanpeng Li <wanpeng.li@linux.intel.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: kernel-team@android.com
> Fixes: 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
> Reported-by: Todd Kjos <tkjos@google.com>
> Signed-off-by: John Stultz <jstultz@google.com>
> ---
>   kernel/sched/deadline.c | 3 ---
>   1 file changed, 3 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index d9d5a702f1a61..566a05efa4e57 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -2501,8 +2501,6 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
>   		return NULL;
>   
>   	next_node = rb_first_cached(&rq->dl.pushable_dl_tasks_root);
> -
> -next_node:
>   	if (next_node) {
>   		p = __node_2_pdl(next_node);
>   
> @@ -2510,7 +2508,6 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
>   			return p;
>   
>   		next_node = rb_next(next_node);
> -		goto next_node;
>   	}
>   
>   	return NULL;

Re: [RFC][PATCH] sched: deadline: Remove unnecessary goto label in pick_earliest_pushable_dl_task

[John Stultz]

On Thu, Dec 5, 2024 at 1:23 PM Christophe JAILLET
<christophe.jaillet@wanadoo.fr> wrote:
>
> Le 05/12/2024 à 22:16, John Stultz a écrit :
> > Commit 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
> > added an odd goto label that seems to be unnecssary, given its
>
> s/unnecssary/unnecessary/
>
> > called unconditionally from the bottom of a while loop and the
> > label is at the top.
>
> Except that it is not a while loop, but only an if.

Ah! Apologies. I need to get my eyes checked. :P  Thank you for
catching me there.

> Maybe, changing this if into a while would save a few lines of code and
> be more readable as-well.

Yeah, Todd pointed out the unconventional usage, but my brain mis-read
the code as being a while(). I'll resend with that change.

thanks
-john

[PATCH v2] sched: deadline: Cleanup goto label in pick_earliest_pushable_dl_task

[John Stultz]

Commit 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
added a goto label seems would be better written as a while
loop.

So replace the goto with a while loop, to make it easier to read.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Wanpeng Li <wanpeng.li@linux.intel.com>
Cc: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc: Todd Kjos <tkjos@google.com>
Cc: kernel-team@android.com
Reported-by: Todd Kjos <tkjos@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
---
v2:
* Corrects my misreading of the code (as pointed out by Christophe
  JAILLET) as already having a while loop, and switches the if to
  a while.
---
 kernel/sched/deadline.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index d9d5a702f1a61..b2cc71984176a 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2501,16 +2501,13 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
 		return NULL;
 
 	next_node = rb_first_cached(&rq->dl.pushable_dl_tasks_root);
-
-next_node:
-	if (next_node) {
+	while (next_node) {
 		p = __node_2_pdl(next_node);
 
 		if (task_is_pushable(rq, p, cpu))
 			return p;
 
 		next_node = rb_next(next_node);
-		goto next_node;
 	}
 
 	return NULL;
-- 
2.47.0.338.g60cca15819-goog

Re: [PATCH v2] sched: deadline: Cleanup goto label in pick_earliest_pushable_dl_task

[K Prateek Nayak]

Hello John,

On 12/6/2024 5:29 AM, John Stultz wrote:
> Commit 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
> added a goto label seems would be better written as a while
> loop.
> 
> So replace the goto with a while loop, to make it easier to read.
> 
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Wanpeng Li <wanpeng.li@linux.intel.com>
> Cc: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: kernel-team@android.com
> Reported-by: Todd Kjos <tkjos@google.com>
> Signed-off-by: John Stultz <jstultz@google.com>

Gave it a spin on my box. Feel free to add:

Reviewed-and-tested-by: K Prateek Nayak <kprateek.nayak@amd.com>

-- 
Thanks and Regards,
Prateek

> ---
> v2:
> * Corrects my misreading of the code (as pointed out by Christophe
>    JAILLET) as already having a while loop, and switches the if to
>    a while.
> ---
>   kernel/sched/deadline.c | 5 +----
>   1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index d9d5a702f1a61..b2cc71984176a 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -2501,16 +2501,13 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
>   		return NULL;
>   
>   	next_node = rb_first_cached(&rq->dl.pushable_dl_tasks_root);
> -
> -next_node:
> -	if (next_node) {
> +	while (next_node) {
>   		p = __node_2_pdl(next_node);
>   
>   		if (task_is_pushable(rq, p, cpu))
>   			return p;
>   
>   		next_node = rb_next(next_node);
> -		goto next_node;
>   	}
>   
>   	return NULL;

Re: [PATCH v2] sched: deadline: Cleanup goto label in pick_earliest_pushable_dl_task

[Juri Lelli]

Hi John,

On 05/12/24 15:59, John Stultz wrote:
> Commit 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
> added a goto label seems would be better written as a while
> loop.
> 
> So replace the goto with a while loop, to make it easier to read.
> 
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Wanpeng Li <wanpeng.li@linux.intel.com>
> Cc: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: kernel-team@android.com
> Reported-by: Todd Kjos <tkjos@google.com>
> Signed-off-by: John Stultz <jstultz@google.com>

Acked-by: Juri Lelli <juri.lelli@redhat.com>

Thanks!
Juri

Re: [PATCH v2] sched: deadline: Cleanup goto label in pick_earliest_pushable_dl_task

[Peter Zijlstra]

On Thu, Dec 05, 2024 at 03:59:35PM -0800, John Stultz wrote:
> Commit 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
> added a goto label seems would be better written as a while
> loop.
> 
> So replace the goto with a while loop, to make it easier to read.
> 

Thanks!

[tip: sched/core] sched: deadline: Cleanup goto label in pick_earliest_pushable_dl_task

[tip-bot2 for John Stultz]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     7675361ff9a1d9038025c05267600d0c762c0236
Gitweb:        https://git.kernel.org/tip/7675361ff9a1d9038025c05267600d0c762c0236
Author:        John Stultz <jstultz@google.com>
AuthorDate:    Thu, 05 Dec 2024 15:59:35 -08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 10 Dec 2024 15:07:06 +01:00

sched: deadline: Cleanup goto label in pick_earliest_pushable_dl_task

Commit 8b5e770ed7c0 ("sched/deadline: Optimize pull_dl_task()")
added a goto label seems would be better written as a while
loop.

So replace the goto with a while loop, to make it easier to read.

Reported-by: Todd Kjos <tkjos@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
Reviewed-and-tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lore.kernel.org/r/20241206000009.1226085-1-jstultz@google.com
---
 kernel/sched/deadline.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 33b4646..643d101 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2516,16 +2516,13 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
 		return NULL;
 
 	next_node = rb_first_cached(&rq->dl.pushable_dl_tasks_root);
-
-next_node:
-	if (next_node) {
+	while (next_node) {
 		p = __node_2_pdl(next_node);
 
 		if (task_is_pushable(rq, p, cpu))
 			return p;
 
 		next_node = rb_next(next_node);
-		goto next_node;
 	}
 
 	return NULL;