From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.snhosting.dk ([87.238.248.203]:18390 "EHLO smtp.domainteam.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751648Ab2DTQVH (ORCPT ); Fri, 20 Apr 2012 12:21:07 -0400 Date: Fri, 20 Apr 2012 18:21:03 +0200 From: Sam Ravnborg Subject: Re: [patch 04/18] smp: Provide generic idle thread allocation Message-ID: <20120420162103.GA3065@merkur.ravnborg.org> References: <20120420122120.097464672@linutronix.de> <20120420124557.102478630@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120420124557.102478630@linutronix.de> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Thomas Gleixner Cc: LKML , linux-arch@vger.kernel.org, Peter Zijlstra , Rusty Russell , "Paul E. McKenney" , Ingo Molnar , "Srivatsa S. Bhat" , Matt Turner , Russell King , Mike Frysinger , Jesper Nilsson , Richard Kuo , Tony Luck , Hirokazu Takata , Ralf Baechle , David Howells , "James E.J. Bottomley" , Benjamin Herrenschmidt , Martin Schwidefsky , Paul Mundt , "David S. Miller" , Chris Metcalf , Richard Weinberger , x86@kernel.org Message-ID: <20120420162103.0Mm8Mxlxh6D5MSJVUjo4c1a80CEOSH-Y4w61MrEzPrA@z> On Fri, Apr 20, 2012 at 01:05:45PM -0000, Thomas Gleixner wrote: > All SMP architectures have magic to fork the idle task and to store it > for reusage when cpu hotplug is enabled. Provide a generic > infrastructure for it. > > Create/reinit the idle thread for the cpu which is brought up in the > generic code and hand the thread pointer to the architecture code via > __cpu_up(). > > Note, that fork_idle() is called via a workqueue, because this > guarantees that the idle thread does not get a reference to a user > space VM. This can happen when the boot process did not bring up all > possible cpus and a later cpu_up() is initiated via the sysfs > interface. In that case fork_idle() would be called in the context of > the user space task and take a reference on the user space VM. > > Signed-off-by: Thomas Gleixner > Cc: Matt Turner > Cc: Russell King > Cc: Mike Frysinger > Cc: Jesper Nilsson > Cc: Richard Kuo > Cc: Tony Luck > Cc: Hirokazu Takata > Cc: Ralf Baechle > Cc: David Howells > Cc: "James E.J. Bottomley" > Cc: Benjamin Herrenschmidt > Cc: Martin Schwidefsky > Cc: Paul Mundt > Cc: "David S. Miller" > Cc: Chris Metcalf > Cc: Richard Weinberger > Cc: x86@kernel.org > --- > arch/Kconfig | 3 + > kernel/cpu.c | 2 - > kernel/sched/core.c | 2 + > kernel/smpboot.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > kernel/smpboot.h | 10 ++++++ > 5 files changed, 99 insertions(+), 1 deletion(-) > > Index: linux-2.6/arch/Kconfig > =================================================================== > --- linux-2.6.orig/arch/Kconfig > +++ linux-2.6/arch/Kconfig > @@ -145,6 +145,9 @@ config HAVE_DMA_ATTRS > config USE_GENERIC_SMP_HELPERS > bool > > +config GENERIC_SMP_IDLE_THREAD > + bool > + Symbols we select in arch Kconfig files are often named HAVE_* And no matter the name - a comment preceeding the definition of the symbol would be nice so it is possible to deduct the use of the symbol in a few years time when this thread is long forgotten. Sam