Date: Mon, 2 Oct 2006 14:01:21 -0700
From: Andrew Morton <akpm@osdl.org>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Ingo Molnar <mingo@elte.hu>, David Howells <dhowells@redhat.com>,
       Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
       linux-arch@vger.kernel.org, Dmitry Torokhov <dtor@mail.ru>,
       Greg KH <greg@kroah.com>, David Brownell <david-b@pacbell.net>,
       Alan Stern <stern@rowland.harvard.edu>
Subject: Re: [PATCH 3/3] IRQ: Maintain regs pointer globally rather than
 passing to IRQ handlers
Message-Id: <20061002140121.f588b463.akpm@osdl.org>
In-Reply-To: <Pine.LNX.4.64.0610021349090.3952@g5.osdl.org>
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	<20061002162053.17763.26032.stgit@warthog.cambridge.redhat.com>
	<20061002132116.2663d7a3.akpm@osdl.org>
	<20061002201836.GB31365@elte.hu>
	<Pine.LNX.4.64.0610021349090.3952@g5.osdl.org>
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On Mon, 2 Oct 2006 13:54:33 -0700 (PDT)
Linus Torvalds <torvalds@osdl.org> wrote:

> 
> 
> On Mon, 2 Oct 2006, Ingo Molnar wrote:
> >
> > i agree that we should do this in one go and in Linus' tree. I suspect 
> > David has a script for this, so we can do it anytime for any tree, 
> > right?
> > 
> > the amount of code that truly relies on regs being present is very low. 
> > Mostly only sysrq type of stuff and the timer interrupt is such.
> 
> Yeah, well, it's been discussed before, and the real problem is not the 
> patch itself, it's the damn drivers maintained outside the tree, and 
> people who want to maintain the same driver for multiple different 
> versions of the kernel.
> 
> Things like the kernel graphics direct-rendering code, for example - 
> mostly maintained in X.org trees that then want to compile with other 
> kernels too.
> 
> I don't personally mind the patch, I just wanted to bring that issue up. 

yup.  Perhaps we could add

#define IRQ_HANDLERS_DONT_USE_PTREGS

so that out-of-tree drivers can reliably do their ifdefing.

> So far, when this has come up, the gains it gives have not been worth the 
> pain. I don't quite see why FRV is so broken that it would matter 20% 
> worth, and I suspect that number was somehow really not real, but more a 
> matter of "this small code snippet that is part of the irq delivery and 
> isn't really measurable improves by 20%", which is a different thing.
> 
> That said, it's almost certainly worth it, and I don't think anybody 
> really objects deep down.
> 
> So if the patch works against my current tree, and nobody objects, I can 
> certainly apply it.
> 
> So speak up, people...
> 

Whimper.   Later in the week, please.
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