From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v4] KVM: Introduce direct MSI message injection for in-kernel irqchips Date: Wed, 04 Apr 2012 14:50:11 +0300 Message-ID: <4F7C3573.7080709@redhat.com> References: <4F734EB3.20500@siemens.com> <4F748AAD.2040103@siemens.com> <4F74B484.30607@siemens.com> <4F7B24EA.2070300@redhat.com> <4F7B29B5.6060703@siemens.com> <20120404083821.GB3003@redhat.com> <4F7C09E7.3020005@redhat.com> <20120404085359.GA3404@redhat.com> <4F7C12E3.3050702@siemens.com> <4F7C161D.3090909@redhat.com> <4F7C16A4.6070303@siemens.com> <4F7C1A7A.5020902@redhat.com> <4F7C26F0.5090901@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , Marcelo Tosatti , kvm , Eric Northup To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:12687 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755807Ab2DDLuT (ORCPT ); Wed, 4 Apr 2012 07:50:19 -0400 In-Reply-To: <4F7C26F0.5090901@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On 04/04/2012 01:48 PM, Jan Kiszka wrote: > > > > I'm not so sure anymore. Sorry about the U turn, but remind me why? In > > the long term it will be slower. > > Likely not measurably slower. If you look at a message through the arch > glasses, you can usually spot the destination directly, specifically if > a message targets a single processor - no need for hashing and table > lookups in the common case. Not on x86. The APIC ID is guest-provided. In x2apic mode it can be quite large. > In contrast, the maintenance costs for the current explicit route based > model are significant as we see now. > You mean in amount of code in userspace? That doesn't get solved since we need to keep compatibility. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.