[PATCH] cpuidle: powerpc: avoid double clear when breaking snooze

[PATCH] cpuidle: powerpc: avoid double clear when breaking snooze

[Shrikanth Hegde]

snooze_loop is done often in any system which has fair bit of
idle time. So it qualifies for even micro-optimizations. 

When breaking the snooze due to timeout, TIF_POLLING_NRFLAG is cleared
twice. Clearing the bit invokes atomics. Avoid double clear and thereby
avoid one atomic write.

dev->poll_time_limit indicates whether the loop was broken due to
timeout. Use that instead of defining a new variable.

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 drivers/cpuidle/cpuidle-powernv.c | 5 ++++-
 drivers/cpuidle/cpuidle-pseries.c | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
index 9ebedd972df0..b89e7111e7b8 100644
--- a/drivers/cpuidle/cpuidle-powernv.c
+++ b/drivers/cpuidle/cpuidle-powernv.c
@@ -95,7 +95,10 @@ static int snooze_loop(struct cpuidle_device *dev,
 
 	HMT_medium();
 	ppc64_runlatch_on();
-	clear_thread_flag(TIF_POLLING_NRFLAG);
+
+	/* Avoid double clear when breaking */
+	if (!dev->poll_time_limit)
+		clear_thread_flag(TIF_POLLING_NRFLAG);
 
 	local_irq_disable();
 
diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
index f68c65f1d023..864dd5d6e627 100644
--- a/drivers/cpuidle/cpuidle-pseries.c
+++ b/drivers/cpuidle/cpuidle-pseries.c
@@ -64,7 +64,10 @@ int snooze_loop(struct cpuidle_device *dev, struct cpuidle_driver *drv,
 	}
 
 	HMT_medium();
-	clear_thread_flag(TIF_POLLING_NRFLAG);
+
+       /* Avoid double clear when breaking */
+	if (!dev->poll_time_limit)
+		clear_thread_flag(TIF_POLLING_NRFLAG);
 
 	raw_local_irq_disable();
 
-- 
2.43.0

Re: [PATCH] cpuidle: powerpc: avoid double clear when breaking snooze

[Mukesh Kumar Chaurasiya]

On Tue, Mar 10, 2026 at 08:58:11PM +0530, Shrikanth Hegde wrote:
> snooze_loop is done often in any system which has fair bit of
> idle time. So it qualifies for even micro-optimizations. 
> 
> When breaking the snooze due to timeout, TIF_POLLING_NRFLAG is cleared
> twice. Clearing the bit invokes atomics. Avoid double clear and thereby
> avoid one atomic write.
> 
> dev->poll_time_limit indicates whether the loop was broken due to
> timeout. Use that instead of defining a new variable.
> 
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
>  drivers/cpuidle/cpuidle-powernv.c | 5 ++++-
>  drivers/cpuidle/cpuidle-pseries.c | 5 ++++-
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
> index 9ebedd972df0..b89e7111e7b8 100644
> --- a/drivers/cpuidle/cpuidle-powernv.c
> +++ b/drivers/cpuidle/cpuidle-powernv.c
> @@ -95,7 +95,10 @@ static int snooze_loop(struct cpuidle_device *dev,
>  
>  	HMT_medium();
>  	ppc64_runlatch_on();
> -	clear_thread_flag(TIF_POLLING_NRFLAG);
> +
> +	/* Avoid double clear when breaking */
> +	if (!dev->poll_time_limit)
> +		clear_thread_flag(TIF_POLLING_NRFLAG);
>  
>  	local_irq_disable();
>  
> diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
> index f68c65f1d023..864dd5d6e627 100644
> --- a/drivers/cpuidle/cpuidle-pseries.c
> +++ b/drivers/cpuidle/cpuidle-pseries.c
> @@ -64,7 +64,10 @@ int snooze_loop(struct cpuidle_device *dev, struct cpuidle_driver *drv,
>  	}
>  
>  	HMT_medium();
> -	clear_thread_flag(TIF_POLLING_NRFLAG);
> +
> +       /* Avoid double clear when breaking */
> +	if (!dev->poll_time_limit)
> +		clear_thread_flag(TIF_POLLING_NRFLAG);
>  
>  	raw_local_irq_disable();
>  
> -- 
> 2.43.0
> 
> 

LGTM

Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>