From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46494) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gOojp-0008UW-BJ for qemu-devel@nongnu.org; Mon, 19 Nov 2018 13:57:38 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gOojk-00085w-8w for qemu-devel@nongnu.org; Mon, 19 Nov 2018 13:57:37 -0500 Received: from mx1.redhat.com ([209.132.183.28]:32962) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gOojk-00085b-3g for qemu-devel@nongnu.org; Mon, 19 Nov 2018 13:57:32 -0500 Date: Mon, 19 Nov 2018 19:56:38 +0100 From: Cornelia Huck Message-ID: <20181119195638.49a9c21e.cohuck@redhat.com> In-Reply-To: <20181119133434-mutt-send-email-mst@kernel.org> References: <20181114233831.10374-1-ehabkost@redhat.com> <20181116034551.GK3807@habkost.net> <20181119114105.4da89f2c.cohuck@redhat.com> <20181119125519-mutt-send-email-mst@kernel.org> <20181119193238.117c2f4e.cohuck@redhat.com> <20181119133434-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH for-4.0 v2] virtio: Provide version-specific variants of virtio PCI devices List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Eduardo Habkost , Andrea Bolognani , qemu-devel@nongnu.org, Gonglei , Paolo Bonzini , Amit Shah , Cleber Rosa , Marcel Apfelbaum , Fam Zheng , Kevin Wolf , Max Reitz , Jason Wang , Wainer dos Santos Moschetta , Philippe =?UTF-8?B?TWF0aGlldS1EYXVkw6k=?= , libvir-list@redhat.com, Markus Armbruster , Laine Stump , Stefan Hajnoczi , Gerd Hoffmann , "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" , Caio Carrara On Mon, 19 Nov 2018 13:42:58 -0500 "Michael S. Tsirkin" wrote: > On Mon, Nov 19, 2018 at 07:32:38PM +0100, Cornelia Huck wrote: > > On Mon, 19 Nov 2018 13:07:59 -0500 > > "Michael S. Tsirkin" wrote: > > > And I strongly believe command line users really really do not want all > > > this mess. Even adding "pci" is the name confuses people (what are the > > > other options?). For command line model=virtio is pretty much perfect. > > > > I'd argue that it's problematic on platforms where you have different > > options for virtio transports. What does "model=virtio" mean? Always > > virtio-pci, if available? Or rather virtio-, with > > being the best option for the machine? > > Most people don't care, for them it's "whatever works". > > We have this assumption that if we force a choice then people will > choose the right thing but in practice they will do what we all do, play > with it until it kind of works and leave well alone afterwards. > That's at best - at worst give up and use an easier tool. That implies that we (the developers) need to care and make sure that "model=virtio" gets them the best possible transport (i.e. on s390x, that would be ccw unless the user explicitly requests pci; I'm not sure what the situation with mmio is -- probably "use pci whenever possible"?) I think that's what libvirt already gives us today (I hope.) What makes it messy on the pci side is that the "best option" actually depends on what kind of guest the user wants to run (if the guest is too old, you're stuck with transitional; if you want to reap the benefits of PCIe, you need non-transitional...)