[PATCH] freezer: Check frozen() before freezing() in freeze_task()

[PATCH] freezer: Check frozen() before freezing() in freeze_task()

[Samuel Wu]

During the freeze stage of suspend, there are multiple passes over the
same list of tasks. Each pass tries to freeze non-frozen tasks, meaning
that the number of frozen tasks increase monotonically, and that each
subsequent pass will mostly be iterating over frozen tasks. Therefore,
it is faster to *first* check that a task is frozen before other checks,
especially since the frozen check is computationally trivial.

Check frozen(p) before !freezing(p) to short circuit the more expensive
freezing_slow_path() calls, while retaining identical return semantics.

On a v7.3 Pixel 9 device, this consistently reduces freeze_processes
latency by ~10% (~4.5 ms).

Signed-off-by: Samuel Wu <wusamuel@google.com>
---
 kernel/freezer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/freezer.c b/kernel/freezer.c
index a76bf957fb32..1adf09321389 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -166,7 +166,7 @@ bool freeze_task(struct task_struct *p)
 	unsigned long flags;
 
 	spin_lock_irqsave(&freezer_lock, flags);
-	if (!freezing(p) || frozen(p) || __freeze_task(p)) {
+	if (frozen(p) || !freezing(p) || __freeze_task(p)) {
 		spin_unlock_irqrestore(&freezer_lock, flags);
 		return false;
 	}
-- 
2.56.0.679.gc527c65306-goog

Re: [PATCH] freezer: Check frozen() before freezing() in freeze_task()

[Bradley Morgan]

On 15 November 2026 00:31:14 GMT, Samuel Wu <wusamuel@google.com> wrote:
>During the freeze stage of suspend, there are multiple passes over the
>same list of tasks. Each pass tries to freeze non-frozen tasks, meaning
>that the number of frozen tasks increase monotonically, and that each
>subsequent pass will mostly be iterating over frozen tasks. Therefore,
>it is faster to *first* check that a task is frozen before other checks,
>especially since the frozen check is computationally trivial.
>
>Check frozen(p) before !freezing(p) to short circuit the more expensive
>freezing_slow_path() calls, while retaining identical return semantics.
>
>On a v7.3 Pixel 9 device, this consistently reduces freeze_processes
>latency by ~10% (~4.5 ms).

7.3 PIXEL 9??? WHAT HOW? THE BASE ON STOCK IS 6.12!!!! WOW! (Please do for
pixel 7, I want flair :c)

>
>Signed-off-by: Samuel Wu <wusamuel@google.com>
>---
> kernel/freezer.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/kernel/freezer.c b/kernel/freezer.c
>index a76bf957fb32..1adf09321389 100644
>--- a/kernel/freezer.c
>+++ b/kernel/freezer.c
>@@ -166,7 +166,7 @@ bool freeze_task(struct task_struct *p)
> 	unsigned long flags;
> 
> 	spin_lock_irqsave(&freezer_lock, flags);
>-	if (!freezing(p) || frozen(p) || __freeze_task(p)) {
>+	if (frozen(p) || !freezing(p) || __freeze_task(p)) {
> 		spin_unlock_irqrestore(&freezer_lock, flags);
> 		return false;
> 	}

Good good.

Reviewed-by: Bradley Morgan <bradley.morgan@linux.dev>


>

--- Thanks!