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From: Andy Lutomirski <luto@amacapital.net>
Date: Mon, 3 Aug 2015 21:07:53 -0700
Message-ID: <CALCETrX2EshRg87fBkHQggRj6kmpVF3+BBSTjsgmdw9A-7MFDQ@mail.gmail.com>
Subject: Re: [PATCH -v2 6/8] jump_label: Add a new static_key interface
To: Borislav Petkov <bp@alien8.de>
Cc: Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Jason Baron <jasonbaron0@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will.deacon@arm.com>, liuj97@gmail.com, rabin@rab.in,
        Ralf Baechle <ralf@linux-mips.org>,
        David Daney <ddaney@caviumnetworks.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        michael@ellerman.id.au, Heiko Carstens <heiko.carstens@de.ibm.com>,
        "David S. Miller" <davem@davemloft.net>
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On Mon, Aug 3, 2015 at 8:37 PM, Borislav Petkov <bp@alien8.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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