Date:	Sat, 23 Jun 2012 18:01:08 -0500
From:	Rob Landley <rob@...dley.net>
To:	Daniel Santos <daniel.santos@...ox.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Christopher Li <sparse@...isli.org>,
	David Daney <david.daney@...ium.com>,
	David Howells <dhowells@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Ingo Molnar <mingo@...nel.org>, Joe Perches <joe@...ches.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-doc@...r.kernel.org, linux-sparse@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Paul Turner <pjt@...gle.com>,
	Pavel Pisa <pisa@....felk.cvut.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Richard Weinberger <richard@....at>,
	Steven Rostedt <rostedt@...dmis.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH v4 0/13] Generic Red-Black Trees

On 06/22/2012 11:00 PM, Daniel Santos wrote:
> Theory of Operation
> ===================
> Historically, genericity in C meant function pointers, the overhead of a
> function call and the inability of the compiler to optimize code across
> the function call boundary.  GCC has been getting better and better at
> optimization and determining when a value is a compile-time constant and
> compiling it out.  As of gcc 4.6, it has finally reached a point where
> it's possible to have generic search & insert cores that optimize
> exactly as well as if they were hand-coded. (see also gcc man page:
> -findirect-inlining)

For those of us who stopped upgrading gcc when it went to a non-open
license, and the people trying to escape to llvm/pcc/open64/tcc/qcc/etc
and build the kernel with that, this will simply be "less optimized"
rather than "you're SOL, hail stallman"?

> Layer 2: Type-Safety
> --------------------
> In order to achieve type-safety of a generic interface in C, we must
> delve deep into the darkened Swamps of The Preprocessor and confront the
> Prince of Darkness himself: Big Ugly Macro.  To be fair, there is an
> alternative solution (discussed in History & Design Goals), the
> so-called "x-macro" or "supermacro" where you #define some pre-processor
> values and include an unguarded header file.  With 17 parameters, I
> choose this solution for its ease of use and brevity, but it's an area
> worth debate.

Because this is just _filling_ me with confidence about portability and
c99 compliance.

(Or I suppose C11!!one! compliance. The new thing that puts asserts in
the base language and makes u8 a keyword since _that_ won't break
existing code and putting utf8 string constants within quotes wasn't
previously possible.)

I'm not saying the standard's perfect, I'm saying a web page that ties
itself to mozilla at the expense of working on firefox, let alone
chrome, might be a bit short-sighted these days. XFree86 begat x.org,
OpenOffice begat libre, etc. The FSF went nuts again and this time
around EGCS is called LLVM, so talking about gcc 4.6-only features
thrills some of us less than you might expect.

I suppose sparse has to be able to cope with this, so that's something...

> To avoid needing multiple versions of the macro, we use a paradigm

Indeed.

I still have trouble remembering how trampolines work when I wander away
for a while. Oh well...

Rob
-- 
GNU/Linux isn't: Linux=GPLv2, GNU=GPLv3+, they can't share code.
Either it's "mere aggregation", or a license violation.  Pick one.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Powered by blists - more mailing lists