linux-kernel - Re: [PATCH 08/35] autonuma: introduce kthread_bind

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Message-ID: <20120529181502.GM21339@redhat.com>
Date:	Tue, 29 May 2012 20:15:02 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH 08/35] autonuma: introduce kthread_bind_node()

On Tue, May 29, 2012 at 07:48:06PM +0200, Peter Zijlstra wrote:
> On Tue, 2012-05-29 at 19:44 +0200, Andrea Arcangeli wrote:
> > 
> > But it'd be totally bad not to do the hard bindings to the cpu_s_ of
> > the node, and not using PF_THREAD_BOUND would just allow userland to
> > shoot itself in the foot. I mean if PF_THREAD_BOUND wouldn't exist
> > already I wouldn't add it, but considering somebody bothered to
> > implement it for the sake to make userland root user "safer", it'd be
> > really silly not to take advantage of that for knuma_migrated too
> > (even if it binds to more than 1 CPU). 
> 
> No, I'm absolutely ok with the user shooting himself in the foot. The
> thing exists because you can crash stuff if you get it wrong with
> per-cpu.
> 
> Crashing is not good, worse performance is his own damn fault.

Some people don't like root to write to /dev/mem or rm -r /
either. I'm not in that camp, but if you're not in that camp, then you
should _never_ care to set PF_THREAD_BOUND, no matter if it's about
crashing or just slowing down the kernel.

If such a thing exists, well using it to avoid the user either to crash or
to screw with the system performance, can only be a bonus.
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