linux-kernel - Re: [PATCH 1/2] sched: Drop the need_resched() loop from cond

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: <1247238045.7529.44.camel@twins>
Date:	Fri, 10 Jul 2009 17:00:45 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched: Drop the need_resched() loop from
 cond_resched()

On Fri, 2009-07-10 at 16:49 +0200, Frederic Weisbecker wrote:
> The schedule() function is a loop that reschedules the current task
> while the TIF_NEED_RESCHED flag is set:
> 
> void schedule(void)
> {
> need_resched:
> 	/* schedule code */
> 	if (need_resched())
> 		goto need_resched;
> }
> 
> And cond_resched() repeat this loop:
> 
> do {
> 	add_preempt_count(PREEMPT_ACTIVE);
> 	schedule();
> 	sub_preempt_count(PREEMPT_ACTIVE);
> } while(need_resched());
> 
> This loop is needless because schedule() already did the check and
> nothing can set TIF_NEED_RESCHED between schedule() exit and the loop
> check in need_resched().
> 
> Then remove this needless loop.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>

Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

> ---
>  kernel/sched.c |    8 +++-----
>  1 files changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 4d1e387..87ecac1 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -6613,11 +6613,9 @@ static void __cond_resched(void)
>  	 * PREEMPT_ACTIVE, which could trigger a second
>  	 * cond_resched() call.
>  	 */
> -	do {
> -		add_preempt_count(PREEMPT_ACTIVE);
> -		schedule();
> -		sub_preempt_count(PREEMPT_ACTIVE);
> -	} while (need_resched());
> +	add_preempt_count(PREEMPT_ACTIVE);
> +	schedule();
> +	sub_preempt_count(PREEMPT_ACTIVE);
>  }
>  
>  int __sched _cond_resched(void)

--
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/