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

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Message-ID: <20120223231842.GA31030@Krystal>
Date:	Thu, 23 Feb 2012 18:18:42 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul Mackerras <paulus@...ba.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jason Baron <jbaron@...hat.com>, a.p.zijlstra@...llo.nl,
	davem@...emloft.net, ddaney.cavm@...il.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/10] jump label: introduce very_[un]likely + cleanups
	+ docs

* Ingo Molnar (mingo@...e.hu) wrote:
> 
> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > So, a modified scheme would be:
> > 
> >         #include <linux/static_key.h>
> > 
> >         struct static_key key = STATIC_KEY_INIT_TRUE;
> > 
> >         if (static_key_false(&key))
> >                 do unlikely code
> >         else
> >                 do likely code
> > 
> > Or:
> > 
> >         if (static_key_true(&key))
> >                 do likely code
> >         else
> >                 do unlikely code
> > 
> > The static key is modified via:
> > 
> >         static_key_slow_inc(&key);
> >         ...
> >         static_key_slow_dec(&key);
> > 
> > Is that API fine? I'll rework the series to such an effect if 
> > everyone agrees.
> 
> I.e. something like the patch below on top of 
> tip:perf/jump-labels.
> 
> Untested - will test it and will refactor the series if 
> everyone's happy.

Hi Ingo,

Reading your documentation updates makes me realise that adding the
"inline" keyword in there would make the whole thing even clearer:

struct static_key key = STATIC_KEY_INLINE_TRUE_INIT;
struct static_key key = STATIC_KEY_INLINE_FALSE_INIT;

static_key_inline_true() / static_key_inline_false()

to show that the "true/false" in there does not mean that the key will
always be true or false (the key value can indeed by changed by calling
static_key_slow_inc/dec), but that the inlined path is either the true
of false branch.

The rest looks fine.

Best regards,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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