linux-kernel - Re: [PATCH 4/4] sched/deadline: use C bitfields for the state flags

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Date:   Fri, 8 Sep 2017 10:24:23 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     luca abeni <luca.abeni@...tannapisa.it>,
        linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH 4/4] sched/deadline: use C bitfields for the state flags

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@...tannapisa.it>

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