Re: [PATCH][2/4] sched: add discrete weighted cpu load function

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Con Kolivas wrote:
On Wednesday 15 March 2006 09:09, Peter Williams wrote:

Con Kolivas wrote:

Peter Williams writes:

Con Kolivas wrote:

+unsigned long weighted_cpuload(const int cpu)
+{
+    return (cpu_rq(cpu)->raw_weighted_load);
+}
+

Wouldn't this be a candidate for inlining?

That would make it unsuitable for exporting via sched.h.

If above_background_load() were implemented inside sched.c instead of in
sched.h there would be no need to export weighted_cpuload() would there?
 This would allow weighted_cpuload() to be inline and the efficiency
would be better as above_background_load() doesn't gain a lot by being
inline


I don't care about above_background_load() being inline; that's done because all functions in header files need to be static inline to not become a mess.


as having weighted_cpulpad() non inline means that it's doing a function call several times in a loop i.e. it may save one function call
by being inline but requires (up to) one function call for every CPU.


I haven't checked but gcc may well inline weighted_cpuload anyway?

It may be doing so for internal uses inside sched.c but I'm pretty sure that it won't for external calls.

We're moving away from inlining most things manually since the compiler is doing it well these days.


OK. Even without explicit inlining you need to give the compiler a chance to optimize function call overhead away. It cant do that with the present arrangement.


The other way around the cost would be just one function call.


The way you're suggesting adds a function that is never used by anything but swap prefetch which would then need to be 'ifdef'ed out to not be needlessly built on every system. Adding ifdefs is frowned upon already, and to have an mm/ specific ifdef in sched.c would be rather ugly.

Sometimes ugliness is the best option.

Peter
--
Peter Williams                                   [email protected]

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce
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