On Fri, Apr 21, 2006 at 01:30:30PM -0700, Vernon Mauery wrote:
> On Friday 21 April 2006 12:22, you wrote:
> > On Fri, Apr 21, 2006 at 05:07:45PM +0200, Jan Engelhardt wrote:
> > > >> Maybe kfree should really be a wrapper around __kfree which does the
> > > >> real work. Then kfree could be a inlined function or a #define that
> > > >> does the NULL pointer check.
> > > >
> > > >NULL pointer check in kfree saves lot of small code fragments in
> > > > callers. It is one of many reasons why kfree does it.
> > > >Making kfree inline wrapper eliminates this save.
> > >
> > > How about
> > >
> > > slab.h:
> > > #ifndef CONFIG_OPTIMIZING_FOR_SIZE
> > > static inline void kfree(const void *p) {
> > > if(p != NULL)
> > > __kfree(p);
> > > }
> > > #else
> > > extern void kfree(const void *);
> > > #endif
> > >
> > > slab.c:
> > > #ifdef CONFIG_OPTIMIZING_FOR_SIZE
> > > void kfree(const void *p) {
> > > if(p != NUILL)
> > > _kfree(p);
> > > }
> > > #endif
> > >
> > > That way, you get your time saving with -O2 and your space saving with
> > > -Os.
> >
> > What makes you confident that the static inline version gives a time
> > saving?
>
> A static inline wrapper would mean that it wouldn't have to make a function
> call just to check if the pointer is NULL. A simple NULL check is faster
> than a function call and then a simple NULL check. In other words, there
> would be no pushing and popping the stack. In almost all cases, replacing an
> inline function with a non-inline function means a trade-off between speed
> and size.
It's not that simple - inline's make the code bigger causing more cache
misses and therefore also having a negative impact on performance.
This is the reason why e.g. the gcc -O3 option usually results in
_worse_ performance than the -O2 option.
> --Vernon
cu
Adrian
BTW: Don't strip the Cc when replying to linux-kernel.
--
"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed
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