linux-kernel - Re: [PATCH 8/9] sched/fair: select idle cpu from idle cpumask for task wakeup

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]

Date:   Fri, 17 Sep 2021 12:15:39 +0800
From:   Barry Song <21cnbao@...il.com>
To:     aubrey.li@...ux.intel.com
Cc:     linux-kernel@...r.kernel.org, mgorman@...hsingularity.net,
        mingo@...nel.org, peterz@...radead.org, song.bao.hua@...ilicon.com,
        valentin.schneider@....com, vincent.guittot@...aro.org,
        yangyicong@...wei.com
Subject: Re: [PATCH 8/9] sched/fair: select idle cpu from idle cpumask for task wakeup

> @@ -4965,6 +4965,7 @@ void scheduler_tick(void)
>
>  #ifdef CONFIG_SMP
> 	rq->idle_balance = idle_cpu(cpu);
> +	update_idle_cpumask(cpu, rq->idle_balance);
>  	trigger_load_balance(rq);
>  #endif
> }

might be stupid, a question bothering yicong and me is that why don't we
choose to update_idle_cpumask() while idle task exits and switches to a
normal task?
for example, before tick comes, cpu has exited from idle, but we are only
able to update it in tick. this makes idle_cpus_span inaccurate, thus we
will scan cpu which isn't actually idle in select_idle_sibling.
is it because of the huge update overhead?

Thanks
barry