Re: [PATCH -v2 6/8] jump_label: Add a new static_key interface

[Peter Zijlstra <peterz@infradead.org>]

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.