From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH 4/6] kvm tools: Add rwlock wrapper
Date: Sun, 29 May 2011 20:12:58 -0700
Message-ID: <20110530031258.GO2668@linux.vnet.ibm.com>
References: <1306511560.3217.23.camel@lappy>
 <20110527171040.GC4356@elte.hu>
 <1306527578.3217.26.camel@lappy>
 <20110528152408.GA27104@elte.hu>
 <1306611908.3282.7.camel@lappy>
 <4DE1EC05.3040001@redhat.com>
 <20110529071948.GA20686@elte.hu>
 <20110529153130.GG2668@linux.vnet.ibm.com>
 <20110529155102.GA6893@linux.vnet.ibm.com>
 <20110529195450.GE13539@elte.hu>
Reply-To: paulmck@linux.vnet.ibm.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Avi Kivity <avi@redhat.com>, Sasha Levin <levinsasha928@gmail.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Pekka Enberg <penberg@kernel.org>, john@jfloren.net,
	kvm@vger.kernel.org, asias.hejun@gmail.com, gorcunov@gmail.com,
	prasadjoshi124@gmail.com
To: Ingo Molnar <mingo@elte.hu>
Return-path: <kvm-owner@vger.kernel.org>
Received: from e7.ny.us.ibm.com ([32.97.182.137]:34922 "EHLO e7.ny.us.ibm.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752611Ab1E3DNE (ORCPT <rfc822;kvm@vger.kernel.org>);
	Sun, 29 May 2011 23:13:04 -0400
Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236])
	by e7.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id p4U2nRoT021556
	for <kvm@vger.kernel.org>; Sun, 29 May 2011 22:49:27 -0400
Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215])
	by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p4U3D37t121454
	for <kvm@vger.kernel.org>; Sun, 29 May 2011 23:13:03 -0400
Received: from d01av01.pok.ibm.com (loopback [127.0.0.1])
	by d01av01.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p4U3D29M002189
	for <kvm@vger.kernel.org>; Sun, 29 May 2011 23:13:03 -0400
Content-Disposition: inline
In-Reply-To: <20110529195450.GE13539@elte.hu>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Sun, May 29, 2011 at 09:54:50PM +0200, Ingo Molnar wrote:
> 
> * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> 
> > And the other reason that you want to mark the readers is for debug 
> > purposes.  Murphy being who he is, you will some day need to check 
> > for someone calling the "OK to update" function while they are 
> > acting as a reader.
> 
> Correct. In one of the previous mails i suggested a debug mode that 
> switches it all to pthread rwlocks.
> 
> We do not want to lose the identify of what the read paths are: this 
> could grow into a BKL-alike nasty-to-fix assumption over a couple of 
> years! Then if someone finds a usecase that intensifies the frequency 
> of one of the key writepaths, we'll be in trouble ...

"BKR" -- Big Kernel Reader!  ;-)

							Thanx, Paul