Messages in this thread |  | | Date | Fri, 24 Feb 2012 10:08:11 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 00/10] jump label: introduce very_[un]likely + cleanups + docs |
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* Jason Baron <jbaron@redhat.com> wrote:
> On Thu, Feb 23, 2012 at 06:18:42PM -0500, Mathieu Desnoyers wrote: > > * Ingo Molnar (mingo@elte.hu) wrote: > > > > > > * Ingo Molnar <mingo@elte.hu> wrote: > > > > > > > So, a modified scheme would be: > > > > > > > > #include <linux/static_key.h> > > > > > > > > struct static_key key = STATIC_KEY_INIT_TRUE; > > > > > > > > if (static_key_false(&key)) > > > > do unlikely code > > > > else > > > > do likely code > > > > > > > > Or: > > > > > > > > if (static_key_true(&key)) > > > > do likely code > > > > else > > > > do unlikely code > > > > > > > > The static key is modified via: > > > > > > > > static_key_slow_inc(&key); > > > > ... > > > > static_key_slow_dec(&key); > > > > > > > > Is that API fine? I'll rework the series to such an effect if > > > > everyone agrees. > > > > > > I.e. something like the patch below on top of > > > tip:perf/jump-labels. > > > > > > Untested - will test it and will refactor the series if > > > everyone's happy. > > > > Hi Ingo, > > > > Reading your documentation updates makes me realise that adding the > > "inline" keyword in there would make the whole thing even clearer: > > > > struct static_key key = STATIC_KEY_INLINE_TRUE_INIT; > > struct static_key key = STATIC_KEY_INLINE_FALSE_INIT; > > > > static_key_inline_true() / static_key_inline_false() > > > > to show that the "true/false" in there does not mean that the key will > > always be true or false (the key value can indeed by changed by calling > > static_key_slow_inc/dec), but that the inlined path is either the true > > of false branch. > > > > Also, as part of the API, there is a test to check the branch > direction - which was 'jump_label_true(key)', but is now also > 'static_key_true(key)', [...]
Yeah, there is such an overlap - I've renamed it to static_key_enabled(), which makes sense anyway as the original was jump_label_enabled()..
Btw., shouldnt it be an inline function? Currently it's:
bool static_key_enabled(struct static_key *key) { return (atomic_read(&key->enabled) > 0); }
which is the perfect candidate for inlining. The difference to static_key_true() is the lack of the jump label patching and the lack of an unlikely() hint.
> [...] so we are going to have to change either the branch site > or the test for true/false name. The above > 'static_key_inline_true/false' solves that.
It's generally good practice to make the mostly commonly used method names the simplest/shortest names - i.e. I don't think we should make it longer via adding an _inline to every use.
In that sense static_key_true() has pretty optimal length - we'd like these tests to also be visually unintrusive.
So in the latest patch (still under testing, will push it out soon) we have:
static_key_true() static_key_false() static_key_enabled()
> Also, I do like having a consistent 'static_key_*' prefix for > the entire API - definitely an improvement for me.
Yeah.
Thanks,
Ingo
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