linux-kernel - Re: RFC [patch] sched: strengthen LAST_BUDDY and minimize buddy induced latencies V3

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 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:	Tue, 20 Oct 2009 06:24:16 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Mike Galbraith <efault@....de>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: RFC [patch] sched: strengthen LAST_BUDDY and minimize buddy
 induced latencies V3

On Sat, 2009-10-17 at 12:24 +0200, Mike Galbraith wrote:
> sched: strengthen LAST_BUDDY and minimize buddy induced latencies.
> 
> This patch restores the effectiveness of LAST_BUDDY in preventing pgsql+oltp
> from collapsing due to wakeup preemption.  It also minimizes buddy induced
> latencies.  x264 testcase spawns new worker threads at a high rate, and was
> being affected badly by NEXT_BUDDY.  It turned out that CACHE_HOT_BUDDY was
> thwarting idle balancing.  This patch ensures that the load can disperse,
> and that buddies can't make any task excessively late.

> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -2007,8 +2007,12 @@ task_hot(struct task_struct *p, u64 now,
>  
>  	/*
>  	 * Buddy candidates are cache hot:
> +	 *
> +	 * Do not honor buddies if there may be nothing else to
> +	 * prevent us from becoming idle.
>  	 */
>  	if (sched_feat(CACHE_HOT_BUDDY) &&
> +			task_rq(p)->nr_running >= sched_nr_latency &&
>  			(&p->se == cfs_rq_of(&p->se)->next ||
>  			 &p->se == cfs_rq_of(&p->se)->last))
>  		return 1;

I'm not sure about this. The sched_nr_latency seems arbitrary, 1 seems
like a more natural boundary.

Also, one thing that arjan found was that we don't need to consider
buddies cache hot if we're migrating them within a cache domain. So we
need to add a SD_flag and sched_domain to properly represent the cache
hierarchy.

--
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/