linux-kernel - Re: [PATCH 3/3] stop_machine: wake up stopper thread lazily

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] [day] [month] [year] [list]

Message-ID: <20130206185213.GC2875@htj.dyndns.org>
Date:	Wed, 6 Feb 2013 10:52:13 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] stop_machine: wake up stopper thread lazily

On Wed, Feb 06, 2013 at 08:40:32PM +0800, Hillf Danton wrote:
> Ring no bell if the stopper thread is busy in handling enqueued works.
> 
> Signed-off-by: Hillf Danton <dhillf@...il.com>
> ---
> 
> --- a/kernel/stop_machine.c	Wed Feb  6 20:05:44 2013
> +++ b/kernel/stop_machine.c	Wed Feb  6 20:06:56 2013
> @@ -72,8 +72,10 @@ static void cpu_stop_queue_work(struct c
>  	spin_lock_irqsave(&stopper->lock, flags);
> 
>  	if (stopper->enabled) {
> +		int wakeup = list_empty(&stopper->works);
>  		list_add_tail(&work->list, &stopper->works);
> -		wake_up_process(stopper->thread);
> +		if (wakeup)
> +			wake_up_process(stopper->thread);

Why does this matter?  It shouldn't matter for correctness.  Is it
meant to be an optimization?  Is it something worth optimizing?  We
hardly ever have contention on cpu stoppers after all and we
shouldn't.

-- 
tejun
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/