From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: spinlock requests (was RE: [Patch] don't spin with
	irq disabled)
Date: Tue, 31 Mar 2009 14:16:11 -0700
Message-ID: <49D2881B.7030303@goop.org>
References: <C5F8423D.6207%keir.fraser@eu.citrix.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xensource.com>
In-Reply-To: <C5F8423D.6207%keir.fraser@eu.citrix.com>
List-Unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Keir Fraser <keir.fraser@eu.citrix.com>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>, Juergen Gross <juergen.gross@fujitsu-siemens.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
List-Id: xen-devel@lists.xenproject.org

Keir Fraser wrote:
> I suspect the existing uses of rwlock in Xen actually are because that
> seemed a natural fit for the code -- obvious split between reader and writer
> critical sections -- rather than because of excessive serialisation if using
> a normal spinlock. I strongly disbelieve that lock acquire/release is a
> significant performance bottleneck for us right now.
>   

Aren't rwlocks sufficiently less efficient than spinlocks that you'd 
tend to use the latter if you don't think contention is an issue?

    J