From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 5/5] ioeventfd: Introduce KVM_IOEVENTFD_FLAG_SOCKET Date: Thu, 14 Jul 2011 15:48:43 +0300 Message-ID: <4E1EE5AB.108@redhat.com> References: <1309927078-5983-1-git-send-email-levinsasha928@gmail.com> <1310276083.2393.6.camel@sasha> <20110710080559.GC1630@redhat.com> <1310469824.2393.22.camel@sasha> <4E1C2F59.90600@redhat.com> <4E1D442E.6090308@redhat.com> <4E1D9623.70801@redhat.com> <4E1D9E75.1070901@redhat.com> <4E1E9A3B.7090200@kernel.org> <4E1EA455.4010608@redhat.com> <4E1EA8A2.9020304@redhat.com> <4E1EBB7A .3030809@redhat.com> <4E1ED913.6070003@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Sasha Levin , "Michael S. Tsirkin" , kvm@vger.kernel.org, Ingo Molnar , Marcelo Tosatti To: Pekka Enberg Return-path: Received: from mx1.redhat.com ([209.132.183.28]:23727 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754564Ab1GNMs6 (ORCPT ); Thu, 14 Jul 2011 08:48:58 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 07/14/2011 03:37 PM, Pekka Enberg wrote: > Hi Avi, > > On Thu, Jul 14, 2011 at 2:54 PM, Avi Kivity wrote: > >> I don't think it needs to be faster for *significant number* of users > >> but yes, I completely agree that we need to make sure KVM gains more > >> than the costs are. > > > > Significant, for me, means it's measured in a percentage, not as digits on > > various limbs. 2% is a significant amount of users. 5 is not. > > Just to make my position clear: I think it's enough that there's one > user that benefits as long as complexity isn't too high and I think > x86/Voyager is a pretty good example of that. So while you can argue > *for* complexity if there are enough users, when there's only few > users, it's really about whether a feature adds significant complexity > or not. Everything adds complexity. And I think x86/voyager was a mistake. > >> We want to use 8250 emulation instead of virtio-serial because it's > >> more compatible with kernel debugging mechanisms. Also, it makes > >> debugging virtio code much easier when we don't need to use virtio to > >> deliver console output while debugging it. We want to make it fast so > >> that we don't need to switch over to another console type after early > >> boot. > >> > >> What's unreasonable about that? > > > > Does virtio debugging really need super-fast serial? Does it need serial at > > all? > > Text mode guests should be super-fast, not virtio debugging. We want > to use 8250 instead of virtio serial or virtio console (which we > support, btw) because it's more compatible with Linux. Debugging > virtio with 8250 has turned out to be useful in the past. Use virtio-console when you're in production (it will be much much faster than socket-mmio 8250), and 8250 when debugging. -- error compiling committee.c: too many arguments to function