linux-kernel - Re: [PATCH -v2 6/8] jump_label: Add a new static

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Message-ID: <CALCETrX2EshRg87fBkHQggRj6kmpVF3+BBSTjsgmdw9A-7MFDQ@mail.gmail.com>
Date:	Mon, 3 Aug 2015 21:07:53 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Jason Baron <jasonbaron0@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>, liuj97@...il.com,
	rabin@....in, Ralf Baechle <ralf@...ux-mips.org>,
	David Daney <ddaney@...iumnetworks.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	michael@...erman.id.au, Heiko Carstens <heiko.carstens@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH -v2 6/8] jump_label: Add a new static_key interface

On Mon, Aug 3, 2015 at 8:37 PM, Borislav Petkov <bp@...en8.de> wrote:
> On Mon, Aug 03, 2015 at 05:57:57PM -0400, Steven Rostedt wrote:
>> That's implementation details, not a general concept that users will
>> need to know about.
>
> Why?
>
> It is a branch, regardless of which insn is used on which arch - it is
> either active and you *branch* to that code or *inactive* and you don't.
> So now it is actually what it should've been from the beginning...

Except that, with the new interface, static_key_likely is the other
way around, right?  If the key is true (i.e. enabled), then it doesn't
branch.

I think of the key as a boolean thing that happens to work by code
patching under the hood.  The fancy patching affects the performance
but doesn't really make it functionally different from a regular
variable.  How about making it extra explicit:

static_key_set(&key, value);

where value is a bool or maybe even an unsigned int?

--Andy
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