From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:53531) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1R0CsQ-0002qN-EL for qemu-devel@nongnu.org; Sun, 04 Sep 2011 09:36:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1R0CsP-0001wD-77 for qemu-devel@nongnu.org; Sun, 04 Sep 2011 09:36:46 -0400 Received: from fmmailgate03.web.de ([217.72.192.234]:56634) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1R0CsO-0001w9-RN for qemu-devel@nongnu.org; Sun, 04 Sep 2011 09:36:45 -0400 Message-ID: <4E637EEA.1030502@web.de> Date: Sun, 04 Sep 2011 15:36:42 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <4E58FC3F.6080809@web.de> <4E5BE7C5.60705@us.ibm.com> <4E5BFF51.9010503@web.de> <4E5C00F0.9070103@redhat.com> <4E5D39C8.5020205@web.de> <4E5E1297.3050904@siemens.com> <4E628607.20309@codemonkey.ws> <4E636B56.9070808@web.de> <4E637E06.9020206@codemonkey.ws> In-Reply-To: <4E637E06.9020206@codemonkey.ws> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig9B357014A60C5D2B121E2776" Sender: jan.kiszka@web.de Subject: Re: [Qemu-devel] [PATCH] pc: Clean up PIC-to-APIC IRQ path List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Lucas Meneghel Rodrigues , Peter Maydell , Anthony Liguori , Marcelo Tosatti , qemu-devel , Blue Swirl , Avi Kivity , Gerd Hoffmann This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig9B357014A60C5D2B121E2776 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 2011-09-04 15:32, Anthony Liguori wrote: > On 09/04/2011 07:13 AM, Jan Kiszka wrote: >> On 2011-09-03 21:54, Anthony Liguori wrote: >>> On 08/31/2011 05:53 AM, Jan Kiszka wrote: >>>> On 2011-08-31 10:25, Peter Maydell wrote: >>>>> On 30 August 2011 20:28, Jan Kiszka wrote: >>>>>> Yes, that's the current state. Once we have bidirectional IRQ >>>>>> links in >>>>>> place (pushing downward, querying upward - required to skip IRQ >>>>>> routers >>>>>> for fast, lockless deliveries), that should change again. >>>>> >>>>> Can you elaborate a bit more on this? I don't think anybody has >>>>> proposed links with their own internal state before in the qdev/qom= >>>>> discussions... >>>> >>>> That basic idea is to allow >>>> >>>> a) a discovery of the currently active IRQ path from source to sink >>>> (that would be possible via QOM just using forward links) >>>> >>>> b) skip updating the states of IRQ routers in the common case, just >>>> signaling directly the sink from the source (to allow in-kernel= >>>> IRQ >>>> delivery or to skip taking some device locks). Whenever some >>>> router >>>> is queried for its current IRQ line state, it would have to ask= >>>> the >>>> preceding IRQ source for its state. So we need a backward link.= >>> >>> Can you provide some concrete use-cases of this? I'm not convinced t= his >>> is really all that important and it seems like tremendous amounts of >>> ugliness would be needed to support it. >> >> INTx support for device assignment, vhost, or any other future in-kern= el >> IRQ sources. >=20 > I prefer to not think of IRQs as special things. They're just single > bits of information that flow through the device model. Having a highe= r > level representation that understands something like paths seems wrong > to me. >=20 > I'd prefer to treat things like device assignment as a hack. You just > need code that can walk the device tree to figure out the path (which i= s > not generic code, it's very machine specific). Then you tell the kerne= l > the resolution of the path and are otherwise completely oblivious in > userspace. See it as you like, but we need the support, not only for device assigment. And I do not see any gain it hacking this instead of designing it. Jan --------------enig9B357014A60C5D2B121E2776 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk5jfuoACgkQitSsb3rl5xRBkQCgoBC4mGbFm0KuhcFogyPls1+d LlEAoIy666Rwa4OySu7NeJvE0jFtCtJ9 =svLW -----END PGP SIGNATURE----- --------------enig9B357014A60C5D2B121E2776--