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

On Sat, 24 Jun 2006, Arjan van de Ven wrote:

> 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...

But doesn't the unlikely help the prediction?  Like I stated, the if may
never succeed.

-- Steve

>
> >  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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