From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:42637) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TLus7-0005mS-5f for qemu-devel@nongnu.org; Wed, 10 Oct 2012 07:54:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TLus1-0006tb-Fx for qemu-devel@nongnu.org; Wed, 10 Oct 2012 07:54:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:23652) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TLus1-0006tW-7y for qemu-devel@nongnu.org; Wed, 10 Oct 2012 07:54:37 -0400 Date: Wed, 10 Oct 2012 13:37:16 +0200 From: "Michael S. Tsirkin" 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-Disposition: inline In-Reply-To: <87wqyz6lf8.fsf@rustcorp.com.au> Subject: Re: [Qemu-devel] Using PCI config space to indicate config location List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Rusty Russell Cc: Anthony Liguori , kvm@vger.kernel.org, qemu-devel , virtualization@lists.linux-foundation.org, Gerd Hoffmann 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