On Fri, 2015-07-17 at 15:44 +0200, Hagen Paul Pfeifer wrote:
> > On July 16, 2015 at 9:23 PM Joe Perches <[email protected]> wrote:
> >
> > It might be useful to have these performance impacting
> > changes guarded by something like CONFIG_CC_OPTIMIZE_FOR_SIZE
> > with another static __always_inline __<func> and a function &
> > EXPORT_SYMBOL or just a static inline so that where code size
> > is critical it's uninlined.
>
> But keep in mind that jhash, jhash2 and __jhash_nwords are *not*
> one-instruction long functions. We duplicate code over and over resulting
> probably in more cache misses. __always_inline__ is probably too strict
> and a vanilla inline is already for 99% of all distribution builds a
> __always_inline__, see ARCH_SUPPORTS_OPTIMIZED_INLINING and
> CONFIG_CC_OPTIMIZE_FOR_SIZE.
Hello.
Perhaps I wasn't clear/explicit enough.
I tried to suggest using a single __always_inline like this:
Two #ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE (or some other
CONFIG_FOO) functions, one in a .h for the existing behavior
and another in a .c for more code space compact uses.
jhash.h
static __always_inline u32 __jhash(const void *key, u32 length, u32 initval)
{
[current jhash implementation...]
}
#ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
u32 jhash(const void *key, u32 length, u32 initval);
#else
static inline u32 jhash(const void *key, u32 length, u32 initval)
{
return __jhash(key, length, initval);
}
#endif
jhash.c:
#ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
u32 jhash(const void *key, u32 length, u32 initval)
{
return __jhash(key, length, initval);
}
EXPORT_SYMBOL(jhash)
#endif
etc...
Perhaps the additional code complexity is not worth it.
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