linux-kernel - Re: [patch 1/3] move WARN

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Date:	Sat, 05 Jan 2008 12:02:37 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 1/3] move WARN_ON() out of line

Jeremy Fitzhardinge wrote:
> 
> Yeah, that seems reasonable if you're optimising for overall size.  Did
> you count the difference of including the function name?  We decided not
> to include it for BUG because its usefulness/size tradeoff didn't seem
> terribly important.

in the WARN_ON case it's not there either, based on Ingo's idea we do a kallsyms lookup
of __builtin_return_address(0) .. same data, less memory.


> But my goal was actually to reduce icache pollution, so by my reckoning
> code bytes were much more expensive than data ones, so putting all BUG
> information in a separate section makes those bytes much less
> significant than putting anything inline in code.  Also, the trap for
> WARN_ON would be smaller than BUG, because it wouldn't need the spurious
> infinite loop needed to make gcc understand the control flow of a BUG.
> 
> On the other hand, you could put the call to out of line warning
> function in a separate section to achieve the same effect.

yeah and gcc even has a compiler option for that. Doubt it's really worth it,
we're still talking a few bytes here ;)

> 
>     J

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