From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758750AbZCAXqc (ORCPT ); Sun, 1 Mar 2009 18:46:32 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751311AbZCAXqW (ORCPT ); Sun, 1 Mar 2009 18:46:22 -0500 Received: from ozlabs.org ([203.10.76.45]:56217 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751335AbZCAXqV (ORCPT ); Sun, 1 Mar 2009 18:46:21 -0500 Subject: Re: [PATCH 1/6] Rewrite MSI-HOWTO From: Michael Ellerman Reply-To: michael@ellerman.id.au To: Matthew Wilcox Cc: Grant Grundler , linux-pci@vger.kernel.org, jbarnes@virtuousgeek.org, linux-kernel@vger.kernel.org, Matthew Wilcox In-Reply-To: <20090227121443.GL16891@parisc-linux.org> References: <1235410082-5016-1-git-send-email-matthew@wil.cx> <1235410082-5016-2-git-send-email-matthew@wil.cx> <20090227061525.GA9883@colo.lackof.org> <20090227121443.GL16891@parisc-linux.org> Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-WZfOc43aXjYJrQ49fcRk" Date: Mon, 02 Mar 2009 10:46:18 +1100 Message-Id: <1235951178.8526.14.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.24.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-WZfOc43aXjYJrQ49fcRk Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Fri, 2009-02-27 at 05:14 -0700, Matthew Wilcox wrote: > On Thu, Feb 26, 2009 at 11:15:25PM -0700, Grant Grundler wrote: > > ... > > > +3. Why use MSIs? > > > + > > > +There are three reasons why using MSIs can give an advantage over > > > +traditional pin-based interrupts. > > ... > > > +PCI devices can only support a single pin-based interrupt per functi= on. > >=20 > > Related to this is a 4th reason: distribute workload across CPUs > > and enables construction of efficient, multi-queue devices. > > Care to mention that? >=20 > That's true for MSI-X, but not for MSIs in general. Workload is already > distributed across CPUs with round-robin interrupts. I'm inclined to > leave out this level of detail. >=20 > > > +The MSI-X capability is much more flexible than the MSI capability. > > > +It supports up to 2048 interrupts, each of which can be separately > > > +assigned. > >=20 > > Nothing describes "assignment" below or what is meant by "assigned". > > My guess is you wanted to differentiate MSIX from MSI with: > > ... and each MSIX can be directed at a different CPU. So might each MSI, depending on the hardware. > > > +5.4. Finding why MSIs are disabled on a device > > > + > > > +From the above three sections, you can see that there are many reaso= ns > > > +why MSIs may not be enabled for a given device. Your first step sho= uld > > > +be to examine your dmesg carefully to determine whether MSIs are ena= bled > > > +for your machine. You should also check your .config to be sure you > > > +have enabled CONFIG_PCI_MSI. > >=20 > > Should mention "fgrep MSI /proc/interrupts" to see if any devices have > > MSI in use? >=20 > Yes, you're right. That won't work on (some) powerpc machines at least .. because MSIs just get routed into the regular PIC. cheers --=20 Michael Ellerman OzLabs, IBM Australia Development Lab wwweb: http://michael.ellerman.id.au phone: +61 2 6212 1183 (tie line 70 21183) We do not inherit the earth from our ancestors, we borrow it from our children. - S.M.A.R.T Person --=-WZfOc43aXjYJrQ49fcRk Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEABECAAYFAkmrHkoACgkQdSjSd0sB4dJ4lACgj6SctuHiUV9fVN7Pe/5oYpyV SqIAoI4tODLQBgnFK9m1TgJzHKxXk8QA =OL2T -----END PGP SIGNATURE----- --=-WZfOc43aXjYJrQ49fcRk--