linux-kernel - Re: [PATCH] cpuidle: menu: Optimize bucket assignment when next_timer_ns equals KTIME

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <0d420c47-f336-41c0-83df-066131338b49@arm.com>
Date: Thu, 3 Apr 2025 10:34:21 +0100
From: Christian Loehle <christian.loehle@....com>
To: Zhongqiu Han <quic_zhonhan@...cinc.com>, rafael@...nel.org,
 daniel.lezcano@...aro.org
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpuidle: menu: Optimize bucket assignment when
 next_timer_ns equals KTIME_MAX

On 4/3/25 10:28, Zhongqiu Han wrote:
> Directly assign the last bucket value instead of calling which_bucket()
> when next_timer_ns equals KTIME_MAX, the largest possible value that
> always falls into the last bucket. This avoids unnecessary calculations
> and enhances performance.
> 
> Signed-off-by: Zhongqiu Han <quic_zhonhan@...cinc.com>

Reviewed-by: Christian Loehle <christian.loehle@....com>

> ---
>  drivers/cpuidle/governors/menu.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
> index 39aa0aea61c6..8fc7fbed0052 100644
> --- a/drivers/cpuidle/governors/menu.c
> +++ b/drivers/cpuidle/governors/menu.c
> @@ -255,7 +255,12 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
>  		 */
>  		data->next_timer_ns = KTIME_MAX;
>  		delta_tick = TICK_NSEC / 2;
> -		data->bucket = which_bucket(KTIME_MAX);
> +		/*
> +		 * Assign the last bucket value directly instead of calling
> +		 * which_bucket(), since KTIME_MAX is the largest possible
> +		 * value that always falls into the last bucket.
> +		 */

comment almost seems overkill.

> +		data->bucket = BUCKETS - 1;
>  	}
>  
>  	if (unlikely(drv->state_count <= 1 || latency_req == 0) ||