From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [RFC][PATCH 28/45] qemu-kvm: msix: Drop tracking of used vectors Date: Tue, 18 Oct 2011 17:55:54 +0200 Message-ID: <4E9DA18A.8040001@siemens.com> References: <20111018115813.GF28776@redhat.com> <4E9D6C5B.8050204@siemens.com> <20111018123305.GK28776@redhat.com> <4E9D734C.2060504@siemens.com> <20111018124818.GO28776@redhat.com> <4E9D786D.4060802@siemens.com> <20111018133719.GS28776@redhat.com> <4E9D831E.100@siemens.com> <20111018140156.GA4980@redhat.com> <4E9D886E.3090201@siemens.com> <20111018150834.GA6103@redhat.com> <4E9D99BE.2030600@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Avi Kivity , Marcelo Tosatti , "kvm@vger.kernel.org" , Alex Williamson , "qemu-devel@nongnu.org" To: "Michael S. Tsirkin" Return-path: Received: from thoth.sbs.de ([192.35.17.2]:21335 "EHLO thoth.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755739Ab1JRP4A (ORCPT ); Tue, 18 Oct 2011 11:56:00 -0400 In-Reply-To: <4E9D99BE.2030600@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On 2011-10-18 17:22, Jan Kiszka wrote: > What KVM has to do is just mapping an arbitrary MSI message > (theoretically 64+32 bits, in practice it's much of course much less) to ( There are 24 distinguishing bits in an MSI message on x86, but that's only a current interpretation of one specific arch. ) > a single GSI and vice versa. As there are less GSIs than possible MSI > messages, we could run out of them when creating routes, statically or > lazily. > > What would probably help us long-term out of your concerns regarding > lazy routing is to bypass that redundant GSI translation for dynamic > messages, i.e. those that are not associated with an irqfd number or an > assigned device irq. Something like a KVM_DELIVER_MSI IOCTL that accepts > address and data directly. This would be a trivial extension in fact. Given its beneficial impact on our GSI limitation issue, I think I will hack up something like that. And maybe this makes a transparent cache more reasonable. Then only old host kernels would force us to do searches for already cached messages. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux