linux-kernel - Re: [PATCH 00/10] jump label: introduce very

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Message-ID: <20120222075334.GA25053@elte.hu>
Date:	Wed, 22 Feb 2012 08:53:34 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Jason Baron <jbaron@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	a.p.zijlstra@...llo.nl, mathieu.desnoyers@...icios.com,
	davem@...emloft.net, ddaney.cavm@...il.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 00/10] jump label: introduce very_[un]likely + cleanups +
 docs


* Ingo Molnar <mingo@...e.hu> wrote:

> But it is fundamentally mixing execution and *data type* and 
> it is not conveying the build time bias properly.
> 
> So the best high level naming would be something like:
> 
> 	struct static_condition static_flag = STATIC_COND_FALSE;
> 
> 
> 	if (very_unlikely(&static_flag)) {
> 		...
> 	}
> 
> 	...
> 
> 	static_cond_inc(&static_flag);
> 	...
> 	static_cond_dec(&static_flag);

Btw., I think the modification path could also carry the high 
cost of modification (stopping all cpus, modifying code, etc.).

This could be done via:

	static_cond_slow_inc(&static_flag);
	...
	static_cond_slow_dec(&static_flag);

And if a developer does not notice that 'slow' implies a 
performance cost, then he probably would have doubly missed this 
aspect of jump_label_inc()/jump_label_dec().

Thanks,

	Ingo
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