From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LLNXI-0004uB-KE for qemu-devel@nongnu.org; Fri, 09 Jan 2009 15:00:52 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LLNXF-0004sD-SO for qemu-devel@nongnu.org; Fri, 09 Jan 2009 15:00:52 -0500 Received: from [199.232.76.173] (port=47913 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LLNXF-0004sA-Np for qemu-devel@nongnu.org; Fri, 09 Jan 2009 15:00:49 -0500 Received: from mail-gx0-f19.google.com ([209.85.217.19]:43943) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1LLNXF-0001sH-4r for qemu-devel@nongnu.org; Fri, 09 Jan 2009 15:00:49 -0500 Received: by gxk12 with SMTP id 12so2133883gxk.10 for ; Fri, 09 Jan 2009 12:00:48 -0800 (PST) Message-ID: <4967ACE8.2030001@codemonkey.ws> Date: Fri, 09 Jan 2009 14:00:40 -0600 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 0/5][RFC] virtio-net: MAC filtering References: <1231349852.7109.79.camel@lappy> <200901091127.32987.paul@codesourcery.com> <4967A84E.9080908@codemonkey.ws> <200901091156.08710.paul@codesourcery.com> In-Reply-To: <200901091156.08710.paul@codesourcery.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paul Brook Cc: Mark McLoughlin , qemu-devel@nongnu.org, Alex Williamson , kvm Paul Brook wrote: >>>> A concern here is the growing size of the virtio-net I/O port space >>>> config. This series brings it up to 256 bytes with PCI resource >>>> >>> This is one reason why IO ports are a reallybad idea. Use memory mapped >>> register spaces like any other sane system and you won't have a problem. >>> >> IO ports are much faster for notification than MMIO in KVM which is why >> the space is currently IO ports. It was never meant to hold very large >> amounts of data. >> > > Huh, I'm surprised it makes any real difference. Other that initial setup, > isn't it just used to "kick" the devieonce after new dscriptors have been > added to the ring buffer? I'd expect to be a fairly expensive operation > (bouncing back to userspace). > It's about 2x as expensive to go to userspace but only probably 1.5x expensive to do MMIO compared to PIO. In the grand scheme of things, I'm not sure that it matters that much. It's relatively simple for someone to try out the change and do some benchmarking. The tougher thing is providing backwards compatible support. Regards, Anthony Liguori > Paul >