linux-kernel - Re: [RFC PATCH 02/15] nohz_task: Avoid nohz task cpu as non-idle timer target

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 for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1292861524.5021.22.camel@laptop>
Date:	Mon, 20 Dec 2010 17:12:04 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 02/15] nohz_task: Avoid nohz task cpu as non-idle
 timer target

On Mon, 2010-12-20 at 11:06 -0500, Steven Rostedt wrote:
> On Mon, 2010-12-20 at 16:47 +0100, Peter Zijlstra wrote:
> > On Mon, 2010-12-20 at 16:24 +0100, Frederic Weisbecker wrote:
> > > Unbound timers are preferably targeted for non idle cpu. If
> > > possible though, prioritize idle cpus over nohz task cpus,
> > > because the main point of nohz task is to avoid unnecessary
> > > timer interrupts.
> > 
> > Oh is it?
> > 
> > I'd very much expect the cpu that arms the timer to get the interrupt. I
> > mean, if the task doesn't want to get interrupted by timers,
> > _DON'T_USE_TIMERS_ to begin with.
> > 
> > So no, don't much like this at all.
> 
> I think this comes from other tasks on other CPUs that are using timers.

Tasks on other CPUs should not cause timers on this CPU, _if_ that does
happen, fix that.

> Although, I'm not sure what causes an "unbound" timer to happen. I
> thought timers usually go off on the CPU that asked for it to go off.

They do, except if you enable some weird power management feature that
migrates timers around so as to let CPUs sleep longer. But I doubt
that's the reason for this here, and if it is, just disable that.

--
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/