linux-kernel - Re: [PATCH] sched: change MAX_SHARES to NR

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Message-ID: <20250812100035.GG4067720@noisy.programming.kicks-ass.net>
Date: Tue, 12 Aug 2025 12:00:35 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: yaozhenguo <yaozhenguo1@...il.com>
Cc: mingo@...hat.com, vincent.guittot@...aro.org,
	linux-kernel@...r.kernel.org, yaozhenguo@...com
Subject: Re: [PATCH] sched: change MAX_SHARES to NR_CPUS

On Tue, Aug 12, 2025 at 05:28:10PM +0800, yaozhenguo wrote:
> From: ZhenguoYao <yaozhenguo1@...il.com>
> 
> As the number of cores in modern CPUs continues to increase,
> 256 * 1024 is no longer sufficient to meet the requirements.
> Therefore, MAX_SHARES is being modified to NR_CPUS * 1024.

You forgot to explain why this needs to scale with CPUs, you also forgot
to provide an argument for why this will not introduce numerical issues.

> Signed-off-by: ZhenguoYao <yaozhenguo1@...il.com>
> ---
>  kernel/sched/sched.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index be9745d104f7..5c219e34f48d 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -510,7 +510,7 @@ struct task_group {
>   *  limitation from this.)
>   */
>  #define MIN_SHARES		(1UL <<  1)
> -#define MAX_SHARES		(1UL << 18)
> +#define MAX_SHARES		(NR_CPUS * 1024UL)
>  #endif
>  
>  typedef int (*tg_visitor)(struct task_group *, void *);
> -- 
> 2.43.5
>