linux-kernel - Re: [PATCH] sched: Optimize branch hint in context

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: <4B128F65.40804@redhat.com>
Date:	Sun, 29 Nov 2009 17:12:37 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Tim Blechmann <tim@...ngt.org>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched: Optimize branch hint in context_switch()

On 11/29/2009 02:01 PM, Tim Blechmann wrote:
> Branch hint profiling on my nehalem machine showed 88%
> incorrect branch hints:
>
> 42017484 326957902  88 context_switch                 sched.c              3043
> 42038493 326953687  88 context_switch                 sched.c              3050
>
> @@ -3040,14 +3040,14 @@ context_switch(struct rq *rq, struct task_struct *prev,
>   	 */
>   	arch_start_context_switch(prev);
>
> -	if (likely(!mm)) {
> +	if (unlikely(!mm)) {
>   		next->active_mm = oldmm;
>   		atomic_inc(&oldmm->mm_count);
>   		enter_lazy_tlb(oldmm, next);
>   	} else
>   		switch_mm(oldmm, mm, next);
>
> -	if (likely(!prev->mm)) {
> +	if (unlikely(!prev->mm)) {
>   		prev->active_mm = NULL;
>   		rq->prev_mm = oldmm;
>   	}
>    

I don't think either the original or the patch is correct.  Whether or 
not a task has an mm is entirely workload dependent, we shouldn't be 
giving hints here.

-- 
error compiling committee.c: too many arguments to function

--
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/