linux-kernel - Re: [PATCH 3/3] IRQ: Maintain regs pointer globally rather than passing to IRQ handlers

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Message-Id: <20061002140121.f588b463.akpm@osdl.org>
Date:	Mon, 2 Oct 2006 14:01:21 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Ingo Molnar <mingo@...e.hu>, David Howells <dhowells@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Dmitry Torokhov <dtor@...l.ru>, Greg KH <greg@...ah.com>,
	David Brownell <david-b@...bell.net>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH 3/3] IRQ: Maintain regs pointer globally rather than
 passing to IRQ handlers

On Mon, 2 Oct 2006 13:54:33 -0700 (PDT)
Linus Torvalds <torvalds@...l.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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