Date: Wed, 29 Jul 2015 10:49:06 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jasonbaron0@gmail.com,
        bp@alien8.de, luto@amacapital.net, tglx@linutronix.de,
        rostedt@goodmis.org, will.deacon@arm.com, liuj97@gmail.com,
        rabin@rab.in, ralf@linux-mips.org, ddaney@caviumnetworks.com,
        benh@kernel.crashing.org, michael@ellerman.id.au,
        heiko.carstens@de.ibm.com, davem@davemloft.net
Subject: Re: [PATCH -v2 6/8] jump_label: Add a new static_key interface
Message-ID: <20150729084906.GH19282@twins.programming.kicks-ass.net>
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 <20150728132313.164884020@infradead.org>
 <55B87E7A.2070509@suse.cz>
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On Wed, Jul 29, 2015 at 09:19:22AM +0200, Vlastimil Babka wrote:

> How would one define a static key that's e.g. expected to be mostly false, but
> with initial value of true, e.g. during boot?

DEFINE_STATIC_KEY_TRUE(blah);

will get you the true at boot time.

You'll then want to use:

	if (static_branch_unlikely(&blah)) {
		/* code that mostly doesn't happen */
	}

To indicate you expect it to be false most of the time. And you'll flip
it to false at runtime using:

	static_branch_disable(&blah);

If GCC co-operates, the body of the branch will be placed out-of-line,
we'll emit a jump to it by default, but once you disable it, we'll nop
the jump and fall straight through.
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