linux-kernel - Re: [PATCH v1 2/9] cpuidle: teo: Reorder candidate state index checks

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: <8959e72a-600d-427a-9ab2-54f14b056766@arm.com>
Date: Wed, 15 Jan 2025 14:46:36 +0000
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>,
 Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
Subject: Re: [PATCH v1 2/9] cpuidle: teo: Reorder candidate state index checks

On 1/13/25 18:36, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Since constraint_idx may be 0, the candidate state index may change to 0
> after assigning constraint_idx to it, so first check if it is greater
> than constraint_idx (and update it if so) and then check it against 0.

So the reason I've left this where it was is because the prev_intercept_idx
was supposed to query the sleep length if we're in an majority-intercept
period and then it makes sense to query the sleep length (to detect such
a period being over).
A constraint_idx == 0 scenario doesn't need the intercept-machinery to
work at all, why are we querying the sleep length then?

> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> This is a rebased variant of
> 
> https://lore.kernel.org/linux-pm/8476650.T7Z3S40VBb@rjwysocki.net/
> 
> ---
>  drivers/cpuidle/governors/teo.c |   15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> --- a/drivers/cpuidle/governors/teo.c
> +++ b/drivers/cpuidle/governors/teo.c
> @@ -428,6 +428,14 @@
>  				break;
>  		}
>  	}
> +
> +	/*
> +	 * If there is a latency constraint, it may be necessary to select an
> +	 * idle state shallower than the current candidate one.
> +	 */
> +	if (idx > constraint_idx)
> +		idx = constraint_idx;
> +
>  	if (!idx && prev_intercept_idx) {
>  		/*
>  		 * We have to query the sleep length here otherwise we don't
> @@ -439,13 +447,6 @@
>  	}
>  
>  	/*
> -	 * If there is a latency constraint, it may be necessary to select an
> -	 * idle state shallower than the current candidate one.
> -	 */
> -	if (idx > constraint_idx)
> -		idx = constraint_idx;
> -
> -	/*

We could leave this here and just do goto end;?