From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus_driver objects Date: Tue, 18 Aug 2009 10:38:39 +0300 Message-ID: <4A8A5A7F.5050809@redhat.com> References: <20090814154125.26116.70709.stgit@dev.haskins.net> <20090814154308.26116.46980.stgit@dev.haskins.net> <20090815103243.GA26749@elte.hu> <4A870964.9090408@codemonkey.ws> <4A8965E0.8050608@gmail.com> <4A89FF08.30509@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Gregory Haskins , Ingo Molnar , Gregory Haskins , kvm@vger.kernel.org, alacrityvm-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, "Michael S. Tsirkin" To: Anthony Liguori Return-path: In-Reply-To: <4A89FF08.30509@codemonkey.ws> Sender: kvm-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 08/18/2009 04:08 AM, Anthony Liguori wrote: > I believe strongly that we should avoid putting things in the kernel > unless they absolutely have to be. I'm definitely interested in > playing with vhost to see if there are ways to put even less in the > kernel. In particular, I think it would be a big win to avoid > knowledge of slots in the kernel by doing ring translation in > userspace. This implies a userspace transition in the fast path. > This may or may not be acceptable. I think this is going to be a very > interesting experiment and will ultimately determine whether my > intuition about the cost of dropping to userspace is right or wrong. I believe with a perfectly scaling qemu this should be feasible. Currently qemu is far from scaling perfectly, but inefficient userspace is not a reason to put things into the kernel. Having a translated ring is also a nice solution for migration - userspace can mark the pages dirty while translating the receive ring. Still, in-kernel translation is simple enough that I think we should keep it. -- error compiling committee.c: too many arguments to function