From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752335AbXC0Dst (ORCPT ); Mon, 26 Mar 2007 23:48:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753231AbXC0Dss (ORCPT ); Mon, 26 Mar 2007 23:48:48 -0400 Received: from ozlabs.org ([203.10.76.45]:33731 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752335AbXC0Dsr (ORCPT ); Mon, 26 Mar 2007 23:48:47 -0400 Subject: Re: [RFC: 2.6.21 patch] let PCI_MSI depend on EXPERIMENTAL From: Michael Ellerman Reply-To: michael@ellerman.id.au To: "Eric W. Biederman" Cc: David Miller , bunk@stusta.de, gregkh@suse.de, linux-kernel@vger.kernel.org, linux-pci@atrey.karlin.mff.cuni.cz In-Reply-To: References: <20070327010247.GW16477@stusta.de> <20070326.182422.115910859.davem@davemloft.net> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-6cUN2o0i6plS+jIFKAiB" Date: Tue, 27 Mar 2007 13:48:45 +1000 Message-Id: <1174967325.5348.21.camel@concordia.ozlabs.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.8.1 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --=-6cUN2o0i6plS+jIFKAiB Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Mon, 2007-03-26 at 21:13 -0600, Eric W. Biederman wrote: > David Miller writes: >=20 > > From: Adrian Bunk > > Date: Tue, 27 Mar 2007 03:02:47 +0200 > > > >> We had during the last months have quite a few MSI bugs and even=20 > >> regressions due to: > >> - core kernel bugs, > >> - device driver bugs and > >> - hardware bugs > - architecture bugs > - MSI enabled on hardware that does not support it. >=20 > aka. Drivers have started supporting MSI, People have started using > and testing MSI, and there has been MSI maintenance. People care. >=20 > The most recent regressions involving MSI have been fixes propagating > their way through the kernel, and I can't think of a one of them > that was MSI specific. Just that the bug didn't happen to show > up clearly without MSI enabled. >=20 > Finding that pci_save_state/pci_restore_state had serious resources > leaks was nasty. >=20 > Finding that pci_enable_device isn't suspend/resume safe as > implemented on x86 and ia64 is very nasty. Currently on x86 it is > only really safe to call pci_enable_device exactly once. But the bugs > are small enough we don't generally notice. >=20 > Personally I prefer glaring outstanding bugs to little subtle once > that only bite you on the second Tuesday of the month. >=20 > The recent MSI maintenance has shifted the code around enough that > problems became visible. I'm not happy with this but I don't expect > this to be an on-going state of affairs. >=20 > >> OTOH, MSI doesn't bring any real advantages for most users. >=20 > So default it to off, although I suspect we are approaching the > point where it would actually be safe to default it to on. We > need a kernel release that doesn't have msi issues yet. >=20 > >> Let's therefore mark PCI_MSI as EXPERIMENTAL. > >>=20 > >> Signed-off-by: Adrian Bunk > > > > This is a good way to ensure that the code doesn't get tested > > enough to ever fix the problems. >=20 > Dave I agreed. PCI_MSI is not the problem. >=20 > I think marking PCI_MSI as EXPERIMENTAL now would be closing the > barn door after the horses have fled. I don't know of a core MSI > code path that hasn't been scrutinized lately. I wouldn't say they > are perfect but they are junk either. Especially given that the > code is not good enough where non x86 architectures can support > MSI. >=20 > There is one big remaining real world problem and that is we enable > MSI optimistically. Resulting in it being enabled on chipsets that > don't support MSI. We still need to change that behavior. I have > been buried in the guts of things so I haven't had the free cycles to > worry about that yet, nor have there been enough people complaining > that it has crossed my pain threshold to just fix the thing. >=20 > I think where we are honestly at is that today MSI works on most new > chipsets. MSI is supported by the hardware. MSI is supported by the > OS. With a little more maturity devices and device drivers will start > taking advantage of in ways that matter to users now that it works. .. and we will start to see more and more hardware that _only_ uses MSI. So we need to get it fixed, rather than sweeping the bugs under the carpet 'til later. 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 --=-6cUN2o0i6plS+jIFKAiB Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (GNU/Linux) iD8DBQBGCJQddSjSd0sB4dIRAmhHAJ9oSWDQ7abErFTLhB/CyR/SaGa45gCeIqO5 ERp+uHQd00nO3ArXLW3aZeY= =SWuO -----END PGP SIGNATURE----- --=-6cUN2o0i6plS+jIFKAiB--