linux-kernel - Re: [PATCH 4/7] sched_ext: Use bitfields for boolean warning flags

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Message-ID: <aNJQFqg2R80VJc7p@gpd4>
Date: Tue, 23 Sep 2025 09:45:26 +0200
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	linux-kernel@...r.kernel.org, sched-ext@...ts.linux.dev
Subject: Re: [PATCH 4/7] sched_ext: Use bitfields for boolean warning flags

On Sun, Sep 21, 2025 at 03:32:43PM -1000, Tejun Heo wrote:
> Convert warned_zero_slice and warned_deprecated_rq in scx_sched struct to
> single-bit bitfields to reduce struct size.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>

Hm... I think the struct size remains the same, at least in my build:
 - before: /* size: 1072, cachelines: 17, members: 14 */
 - after:  /* size: 1072, cachelines: 17, members: 14 */

Maybe if we add more attributes in the future?

Thanks,
-Andrea

> ---
>  kernel/sched/ext_internal.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/ext_internal.h b/kernel/sched/ext_internal.h
> index 2e289931e567..1a80d01b1f0c 100644
> --- a/kernel/sched/ext_internal.h
> +++ b/kernel/sched/ext_internal.h
> @@ -871,8 +871,8 @@ struct scx_sched {
>  	struct scx_dispatch_q	**global_dsqs;
>  	struct scx_sched_pcpu __percpu *pcpu;
>  
> -	bool			warned_zero_slice;
> -	bool			warned_deprecated_rq;
> +	bool			warned_zero_slice:1;
> +	bool			warned_deprecated_rq:1;
>  
>  	atomic_t		exit_kind;
>  	struct scx_exit_info	*exit_info;
> -- 
> 2.51.0
>