Re: [dpdk-dev] [PATCH v7 4/8] vhost: rxtx: use queue id instead of constant ring index

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 21 Oct 2015 09:38:37 +0000
"Ananyev, Konstantin" <konstantin.ananyev@intel.com> wrote:

> > > minor nits:
> > >  * this doesn't need to be marked as always inline,
> > >     that is as they say in English "shooting a fly with a bazooka"  
> > Stephen:
> > always_inline "forces" the compiler to inline this function, like a macro.
> > When should it be used or is it not preferred at all?  
> 
> I also don't understand what's wrong with using 'always_inline' here.
> As I understand the author wants compiler to *always inline* that function.
> So seems perfectly ok to use it here.
> As I remember just 'inline' is sort of recommendation that compiler is free to ignore.
> Konstantin 

I follow Linux/Linus advice and resist the urge to add strong inlining.
The compiler does a good job of deciding to inline, and many times
the reason it chooses for not inlining are quite good like:
  - the code is on an unlikely branch
  - register pressure means inlining would mean the code would be worse

Therefore my rules are:
  * only use inline for small functions. Let compiler decide on larger static funcs
  * write code where most functions are static (localized scope) where compiler
    can decide
  * reserve always inline for things that access hardware and would break if not inlined.