lkml.org 
[lkml]   [2006]   [Jun]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] ext3_clear_inode(): avoid kfree(NULL)
FromArjan van de Ven <>
DateSat, 24 Jun 2006 14:46:17 +0200
On Sat, 2006-06-24 at 08:33 -0400, Steven Rostedt wrote:
> 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?

nope none at all, at least not on x86/x86-64.
(in fact there is no way to help the prediction on those architectures
that actually works)

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-06-24 14:48    [from the cache]
©2003-2010