From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [Qemu-devel] Using PCI config space to indicate config location Date: Wed, 10 Oct 2012 13:37:16 +0200 Message-ID: <20121010113716.GA5737@redhat.com> References: <87bogddq0l.fsf@codemonkey.ws> <5072EA14.30809@redhat.com> <87k3v1gfw1.fsf@codemonkey.ws> <507333F1.1060000@redhat.com> <874nm4u1in.fsf@codemonkey.ws> <87sj9o8qn7.fsf@rustcorp.com.au> <87sj9oh0pm.fsf@codemonkey.ws> <87haq48hds.fsf@rustcorp.com.au> <874nm3ycj8.fsf@codemonkey.ws> <87wqyz6lf8.fsf@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <87wqyz6lf8.fsf@rustcorp.com.au> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Rusty Russell Cc: Anthony Liguori , kvm@vger.kernel.org, Benjamin Herrenschmidt , qemu-devel , virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Wed, Oct 10, 2012 at 02:14:11PM +1030, Rusty Russell wrote: > > See above. A guest could happily just use BAR1/BAR2 and completely > > ignore BAR0 provided that BAR1/BAR2 are present. > > But x86 guests want BAR0 because IO space is faster than MMIO. Right? Or to be a bit more precise, ATM on x86 emulating IO instructions is faster than MMIO. IIUC this is since you get the address/data in registers and don't need to decode them. -- MST