linux-kernel - Re: [PATCH 5 of 7] x86/paravirt: add register-saving thunks to reduce caller register pressure

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Date:	Fri, 06 Feb 2009 08:37:21 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Ingo Molnar <mingo@...e.hu>, Zachary Amsden <zach@...are.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ian Campbell <ian.campbell@...rix.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-kernel@...r.kernel.org,
	Ravikiran Thirumalai <kiran@...lemp.com>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH 5 of 7] x86/paravirt: add register-saving thunks to reduce
 caller register pressure

Andi Kleen wrote:
> I had something like this (but not as generic) for the old pre
> unification semaphores on x86-64 too. I think it's a generally useful
> facility for lots of things (in fact I've been asking gcc developers
> for providing this in a general way for some time).
>   

What other users do you have in mind?

> So I would suggest to move the necessary macros to do that outside
> paravirt.h into a separate include so that it can be used independently
> and not call it PV_*.

That wouldn't be too hard to do, but I don't think its something we 
should do lightly.  There are quite a few pitfalls, and the bugs can get 
pretty obscure.  It would also mean bringing out a lot of the PV_CALL 
machinery, and I'm not sure we really want to give that too much 
exposure in the light of day.

    J

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