Re: [PATCH 00/10] jump label: introduce very_[un]likely + cleanups +docs

[Ingo Molnar]

* H. Peter Anvin <hpa@xxxxxxxxx> wrote:

> Stupid thought... do we have cases that matter where the bias 
> and default don't agree?

Yeah, that was one of my worries about the proposed original 
tongue twisters (see Jason's original series: "jump label: 
introduce default true branch").

For example could you tell *at a glance* what this does:

+       if (!static_branch_def_false(&perf_sched_events.key))

?

I certainly couldn't, I'd have to consider the '!', that it's a 
'static branch' and that it's either 'defined to false' or 
'default to false'.

Linguistic and visual barriers all around, and that's for code 
that I am intimately familar with ...

The problem with static_branch_def_false/def_true was that the 
very intuitively visible bias that we see with 
likely()/unlikely() is confused in jump label constructs through 
two layers of modifiers. And the fix is so easy, a simple rename 
in most cases ;-)

So instead of that, in this series we have:

+       if (very_unlikely(&perf_sched_events.key))

which is a heck of an improvement IMO. I'd still up its 
readability a notch, by also signalling the overhead of the 
update path by making it:

+       if (very_unlikely(&perf_sched_events.slow_flag))

... but I don't want to be that much of a readability nazi ;-)

Thanks,

	Ingo
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