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

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Message-ID: <7479958c-1932-4ced-a7a4-53ac6ea3a38e@email.android.com>
Date:	Wed, 22 Feb 2012 00:01:03 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>
CC:	Jason Baron <jbaron@...hat.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

Stupid thought... do we have cases that matter where the bias and default don't agree?

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

>
>* 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

-- 
Sent from my mobile phone. Please excuse my brevity and lack of formatting.
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