linux-kernel - Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

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Date:	Fri, 9 Jan 2009 13:46:55 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	paulmck@...ux.vnet.ibm.com, Gregory Haskins <ghaskins@...ell.com>,
	Matthew Wilcox <matthew@....cx>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>,
	Peter Morreale <pmorreale@...ell.com>,
	Sven Dietrich <SDietrich@...ell.com>
Subject: Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning



On Fri, 9 Jan 2009, Ingo Molnar wrote:
> 
> - Perhaps we could introduce a name for the first category: __must_inline? 
>   __should_inline? Not because it wouldnt mean 'always', but because it is 
>   'always inline' for another reason than the correctless __always_inline.

I think you're thinking about this the wrong way.

"inline" is a pretty damn strong hint already.

If you want a weaker one, make it _weaker_ instead of trying to use 
superlatives like "super_inline" or "must_inline" or whatever.

So I'd suggest:

 - keep "inline" as being a strong hint. In fact, I'd suggest it not be a 
   hint at all - when we say "inline", we mean it. No ambiguity 
   _anywhere_, and no need for idiotic "I really really REALLY mean it" 
   versions.

 - add a "maybe_inline" or "inline_hint" to mean that "ok, compiler, maybe 
   this is worth inlining, but I'll leave the final choice to you".

That would get rid of the whole rationale for OPTIMIZE_INLINING=y, because 
at that point, it's no longer potentially a correctness issue. At that 
point, if we let gcc optimize things, it was a per-call-site conscious 
decision.

			Linus
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