linux-kernel - Re: [PATCH] memcg: remove unneeded preempt

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Message-ID: <alpine.DEB.2.00.1108251009120.27407@router.home>
Date:	Thu, 25 Aug 2011 10:11:50 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Thelen <gthelen@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] memcg: remove unneeded preempt_disable

On Thu, 25 Aug 2011, Peter Zijlstra wrote:

> On Thu, 2011-08-18 at 14:40 -0700, Andrew Morton wrote:
> >
> > I think I'll apply it, as the call frequency is low (correct?) and the
> > problem will correct itself as other architectures implement their
> > atomic this_cpu_foo() operations.
>
> Which leads me to wonder, can anything but x86 implement that this_cpu_*
> muck? I doubt any of the risk chips can actually do all this.
> Maybe Itanic, but then that seems to be dying fast.

The cpu needs to have an RMW instruction that does something to a
variable relative to a register that points to the per cpu base.

Thats generally possible. The problem is how expensive the RMW is going to
be.

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