From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [Qemu-devel] [RFC v2 00/20] Memory API Date: Mon, 27 Jun 2011 15:28:05 -0500 Message-ID: <4E08E7D5.4000207@codemonkey.ws> References: <1309180927-19003-1-git-send-email-avi@redhat.com> <4E089DFF.3090401@redhat.com> <20110627155216.GA5614@redhat.com> <4E08A79D.7010606@redhat.com> <20110627155920.GB5614@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Avi Kivity , qemu-devel@nongnu.org, kvm@vger.kernel.org To: "Michael S. Tsirkin" Return-path: Received: from mail-pw0-f46.google.com ([209.85.160.46]:48550 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754307Ab1F0U2J (ORCPT ); Mon, 27 Jun 2011 16:28:09 -0400 Received: by pwj7 with SMTP id 7so3165582pwj.19 for ; Mon, 27 Jun 2011 13:28:09 -0700 (PDT) In-Reply-To: <20110627155920.GB5614@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 06/27/2011 10:59 AM, Michael S. Tsirkin wrote: > On Mon, Jun 27, 2011 at 06:54:05PM +0300, Avi Kivity wrote: >> On 06/27/2011 06:52 PM, Michael S. Tsirkin wrote: >>> - bridges might also enable subtractive decoding >>> (required for isa behind the bridge) >> >> What does that mean? > > subtractive decoding is > a method of address decoding in which a device accepts all > accesses not positively decoded by another agent. Subtractive decoding is very slow in real hardware so generally any well known devices are positively decoded (like anything on the Super I/O chip). Unless we're dealing with very odd ISA devices, we probably don't need to worry about subtractive decoding. The real key point is, each level may dispatch in subtly different ways. You can get 95% of the way there with a generic memory API. I think it's the 95% that actually matters but just realize that we can't model hardware exactly without true hierarchical dispatch. Regards, Anthony Liguori