linux-kernel - Re: [PATCH v2 1/4] sched/fair: Optimize checking for group_asym

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: <YI/BSZ9OkOqCp/0F@hirez.programming.kicks-ass.net>
Date:   Mon, 3 May 2021 11:24:25 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...nel.org>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.comi>, Mel Gorman <mgorman@...e.de>,
        Len Brown <len.brown@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        Quentin Perret <qperret@...gle.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, Aubrey Li <aubrey.li@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH v2 1/4] sched/fair: Optimize checking for
 group_asym_packing

On Tue, Apr 13, 2021 at 07:04:33PM -0700, Ricardo Neri wrote:
> By checking local_group, we can avoid additional checks and invoking
> sched_asmy_prefer() when it is not needed.

This really could do with a few words on *why* that is correct. ISTR
thinking this made sense when I last looked at it, but today, after
having the brain reset by not looking at a computer for 4 days its not
immediate obvious anymore.

> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 04a3ce20da67..4ef3fa0d5e8d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8455,7 +8455,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
>  	}
>  
>  	/* Check if dst CPU is idle and preferred to this group */
> -	if (env->sd->flags & SD_ASYM_PACKING &&
> +	if (!local_group && env->sd->flags & SD_ASYM_PACKING &&
>  	    env->idle != CPU_NOT_IDLE &&
>  	    sgs->sum_h_nr_running &&
>  	    sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu)) {
> -- 
> 2.17.1
>