Message-ID: <alpine.LNX.2.00.1010182342120.31740@banach.math.auburn.edu>
Date:	Tue, 19 Oct 2010 00:00:58 -0500 (CDT)
From:	Theodore Kilgore <kilgota@...ach.math.auburn.edu>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Dave Airlie <airlied@...il.com>, Greg KH <greg@...ah.com>,
	codalist@...emann.coda.cs.cmu.edu, autofs@...ux.kernel.org,
	Samuel Ortiz <samuel@...tiz.org>, Jan Kara <jack@...e.cz>,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
	Arnd Bergmann <arnd@...db.de>,
	Jan Harkes <jaharkes@...cmu.edu>, netdev@...r.kernel.org,
	Anders Larsen <al@...rsen.net>, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	Bryan Schumaker <bjschuma@...app.com>,
	Christoph Hellwig <hch@...radead.org>,
	ksummit-2010-discuss@...ts.linux-foundation.org,
	Petr Vandrovec <vandrove@...cvut.cz>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-fsdevel@...r.kernel.org,
	Evgeniy Dushistov <dushistov@...l.ru>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Hendry <andrew.hendry@...il.com>,
	linux-media@...r.kernel.org
Subject: Re: [Ksummit-2010-discuss] [v2] Remaining BKL users, what to do



On Mon, 18 Oct 2010, Steven Rostedt wrote:

> On Tue, 2010-10-19 at 12:45 +1000, Dave Airlie wrote:
> > On Tue, Oct 19, 2010 at 12:24 PM, Greg KH <greg@...ah.com> wrote:
> 
> > > So, there is no need for the i830 driver?  Can it just be removed
> > > because i915 works instead?
> > 
> > No because it provides a different userspace ABI to the i915 driver to
> > a different userspace X driver etc.
> > 
> > like I'm sure the intersection of this driver and reality are getting
> > quite limited, but its still a userspace ABI change and needs to be
> > treated as such. Xorg 6.7 and XFree86 4.3 were the last users of the
> > old driver/API.
> 
> Thus, you are saying that this will break for people with older user
> apps and have a newer kernel?
> 
> > 
> > >> So it really only leaves the problem case of what do distros do if we
> > >> mark things as BROKEN_ON_SMP, since no distro builds UP kernels and
> > >> when you boot the SMP kernels on UP they don't run as SMP so not
> > >> having the driver load on those is a problem. Maybe we just need some
> > >> sort of warn on smp if a smp unfriendly driver is loaded and we
> > >> transition to SMP mode. Though this sounds like either (a) something
> > >> we do now and I don't about it, (b) work.
> > >
> > > So you are saying that just because distros will never build such a
> > > thing, we should keep it building for SMP mode?  Why not prevent it from
> > > being built and if a distro really cares, then they will pony up the
> > > development to fix the driver up?
> > 
> > Distros build the driver now even it it didn't work on SMP it wouldn't
> > matter to the 99% of people who have this hw since it can't suppport
> > SMP except in some corner cases. So not building for SMP is the same
> > as just throwing it out of the kernel since most people don't run
> > kernel.org kernels, and shouldn't have to just to get a driver for
> > some piece of hardware that worked fine up until now.
> 
> Ah! Exactly! Thus, those that do not run kernel.org kernels are using a
> distro kernel. Wont these same people use the distro userspace? That is,
> if they have upgraded their kernel, most likely, they also update their
> X interface.
> 
> > 
> > Look at this from a user who has this hardware pov, it works for them
> > now with a distro kernel, us breaking it isn't going to help that user
> > or make any distro care, its just going to screw over the people who
> > are actually using it.
> 
> But they can use the i915 driver instead, because they are using the
> newer userspace apps.
> 
> > 
> > > In other words, if someone really cares, then they will do the work,
> > > otherwise why worry?  Especially as it seems that no one here is going
> > > to do it, right?
> > 
> > Well the thing is doing the work right is a non-trivial task and just
> > dropping support only screws the people using the hardware,
> > it doesn't place any burden on the distro developers to fix it up. If
> > people are really serious about making the BKL go away completely, I
> > think the onus should be on them to fix the drivers not on the users
> > who are using it, like I'm  guessing if this gets broken the bug will
> > end up in Novell or RH bugzilla in a year and nobody will ever see it.
> 
> Well the problem comes down to testing it. I don't know of any developer
> that is removing the BKL that actually owns hardware to test out these
> broken drivers. And for the change not being trivial, means that there's
> no way to do in correctly.
> 
> -- Steve

I might be able to find some hardware still lying around here that uses an 
i810. Not sure unless I go hunting it. But I get the impression that if 
the kernel is a single-CPU kernel there is not any problem anyway? Don't 
distros offer a non-smp kernel as an installation option in case the user 
needs it? So in reality how big a problem is this?

Theodore Kilgore
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