linux-kernel - Re: [patch 06/10] Immediate Value

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Message-ID: <468ABFE0.5090902@zytor.com>
Date:	Tue, 03 Jul 2007 14:30:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 06/10] Immediate Value - i386 Optimization

Mathieu Desnoyers wrote:
> 
> If we can change the compiler, here is what we could do:
> 
> Tell GCC to put NOPs that could be altered by a branch alternative to
> some specified code. We should be able to get the instruction pointers
> (think of inlines) to these nop/branch instructions so we can change
> them dynamically.
> 

Changing the compiler should be perfectly feasible, *BUT* I think we
need a transitional solution that works on existing compilers.

> I suspect this would be inherently tricky. If someone is ready to do
> this and tells me "yes, it will be there in 1 month", I am more than
> ready to switch my markers to this and help, but since the core of my
> work is kernel tracing, I don't have the time nor the ressources to
> tackle this problem.
> 
> In the event that someone answers "we'll do this in the following 3
> years", I might consider to change the if (immediate(var)) into an
> immediate_if (var) so we can later proceed to the change with simple
> ifdefs without rewriting all the kernel code that would use it.

This is much more of "we'll do that in the following 1-2 years", since
we have to deal with a full gcc development cycle.  However, I really
want to see this being implemented in a way that would let us DTRT in
the long run.

	-hpa
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