Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)

[Adrian Bunk <bunk@stusta.de>]

On Thu, Apr 27, 2006 at 11:08:05AM +0200, Arjan van de Ven wrote:
> On Thu, 2006-04-27 at 10:56 +0200, Adrian Bunk wrote:
> > On Thu, Apr 27, 2006 at 10:41:12AM +0200, Arjan van de Ven wrote:
> > > On Thu, 2006-04-27 at 10:31 +0200, Adrian Bunk wrote:
> > > > On Thu, Apr 27, 2006 at 08:50:40AM +0200, Arjan van de Ven wrote:
> > > > > On Thu, 2006-04-27 at 09:28 +0300, Pekka J Enberg wrote:
> > > > > > On Thu, 27 Apr 2006, Nick Piggin wrote:
> > > > > > > Not to dispute your conclusions or method, but I think doing a
> > > > > > > defconfig or your personal config might be more representative
> > > > > > > of % size increase of text that will actually be executed. And
> > > > > > > that is the expensive type of text.
> > > > > > 
> > > > > > True but I was under the impression that Arjan thought we'd get text 
> > > > > > savings with GCC 4.1 by making kfree() inline.
> > > > > 
> > > > > not savings in text size, I'll settle for the same size.
> > > > >...
> > > > 
> > > > It will always be bigger since there are cases where it's unknown at 
> > > > compile time whether it will be NULL when called.
> > > 
> > > if it's "unknown" you could call into a separate kfree() which does
> > > check out of line. (sure that's a dozen bytes bigger but that is
> > > noise ;)
> > 
> > It's noise and _much work.
> 
> not if the compiler can do it. The *compiler* knows a lot (4.1 at
> least)..

But for using your suggested "separate kfree() which does check out of 
line" for not having the (otherwise unavoidable) space increast, we have 
to manually change kfree() callers.

My main question repeated:
Do you have any benchmarks where your approach brings a measurable
benefit? I wouldn't have expected kfree() being in many hotpaths.

cu
Adrian

-- 

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       "Only a promise," Lao Er said.
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