Re: [PATCH] ext3_clear_inode(): avoid kfree(NULL)

On Sat, 2006-06-24 at 08:20 -0400, Steven Rostedt wrote:
> On Sat, 24 Jun 2006, Arjan van de Ven wrote:
> 
> >
> > >
> > > Because at that callsite, NULL is the common case.  We avoid a do-nothing
> > > function call most of the time.  It's a nano-optimisation.
> >
> > but a function call is basically free, while an if () is not... even
> > with unlikely()...
> >
> > sounds like a misoptimization to me.
> >
> 
> How is a function call free when an if is not? 

in general, a function call is 100% predictable without any real control
flow dependencies for the processor, and thus there is no real issue in
the execution pipeline. An if is a conditional branch, which breaks up
the execution pipeline if mispredicted...

>  Especially if that
> function does the exact same if?

sure; 

but to call this code an optimization ... it's just extra code.


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