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[PATCH 4/4] sched/deadline: use C bitfields for the state flags

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  [PATCH 4/4] sched/deadline: use C bitfields for the state flags luca abeni <luca.abeni@santannapisa.it> - 2017-09-07 12:20 +0200
    Re: [PATCH 4/4] sched/deadline: use C bitfields for the state flags Daniel Bristot de Oliveira <bristot@redhat.com> - 2017-09-08 10:30 +0200

#1728116 — [PATCH 4/4] sched/deadline: use C bitfields for the state flags

Ask the compiler to use a single bit for storing true / false values,
instead of wasting the size of a whole int value.
Tested with gcc 5.4.0 on x86_64, and the compiler produces the expected
Assembly (similar to the Assembly code generated when explicitly accessing
the bits with bitmasks, "&" and "|").

Signed-off-by: luca abeni <luca.abeni@santannapisa.it>
---
 include/linux/sched.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 68b3833..e03cc69 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -472,10 +472,10 @@ struct sched_dl_entity {
 	 * conditions between the inactive timer handler and the wakeup
 	 * code.
 	 */
-	int				dl_throttled;
-	int				dl_boosted;
-	int				dl_yielded;
-	int				dl_non_contending;
+	int				dl_throttled      : 1;
+	int				dl_boosted        : 1;
+	int				dl_yielded        : 1;
+	int				dl_non_contending : 1;
 
 	/*
 	 * Bandwidth enforcement timer. Each -deadline task has its
-- 
2.7.4

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#1728685

On 09/07/2017 12:09 PM, luca abeni wrote:
> Ask the compiler to use a single bit for storing true / false values,
> instead of wasting the size of a whole int value.
> Tested with gcc 5.4.0 on x86_64, and the compiler produces the expected
> Assembly (similar to the Assembly code generated when explicitly accessing
> the bits with bitmasks, "&" and "|").
> 
> Signed-off-by: luca abeni <luca.abeni@santannapisa.it>

Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>

-- Daniel
> ---
>  include/linux/sched.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 68b3833..e03cc69 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -472,10 +472,10 @@ struct sched_dl_entity {
>  	 * conditions between the inactive timer handler and the wakeup
>  	 * code.
>  	 */
> -	int				dl_throttled;
> -	int				dl_boosted;
> -	int				dl_yielded;
> -	int				dl_non_contending;
> +	int				dl_throttled      : 1;
> +	int				dl_boosted        : 1;
> +	int				dl_yielded        : 1;
> +	int				dl_non_contending : 1;
>  
>  	/*
>  	 * Bandwidth enforcement timer. Each -deadline task has its
> 

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