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

[Steven Rostedt]

On Wed, 29 Jul 2015 10:49:06 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> 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);

I wonder if static_branch_set_false(&blah) would be a better name to
understand. What does "disable" / "enable" mean?

If we declare it "TRUE" when defining it, it only makes sense to change
it to "false" later on.

-- Steve


> 
> 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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