From: Jeremy Fitzhardinge Subject: Re: [patch 2/8] Implement always-locked bit ops, for memory shared with an SMP hypervisor. Date: Wed, 02 Aug 2006 17:35:56 -0700 Message-ID: <44D144EC.3000205@goop.org> References: <20060803002510.634721860@xensource.com> <20060803002518.061401577@xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Christoph Lameter Cc: Jeremy Fitzhardinge , akpm@osdl.org, linux-kernel@vger.kernel.org, virtualization@lists.osdl.org, xen-devel@lists.xensource.com, Ian Pratt , Christian Limpach , Chris Wright List-Id: xen-devel@lists.xenproject.org Christoph Lameter wrote: > I think I asked this before.... > > Would it not be simpler to always use the locked implementation on UP? At > least when the kernel is compiled with hypervisor support? This is going > to add yet another series of bit operations You mean make the standard bit-ops atomic on UP when compiling for CONFIG_PARAVIRT? We think its too much of a burden; there are only a few operations which must be locked in the hypervisor case, and bit ops are used everywhere. I'd like to get it to the point where there's no significant overhead in configuring for PARAVIRT, even if you run on native hardware. J