Re: [dpdk-dev] [PATCH v2 1/2] ethdev: add buffered tx api

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-03-09 15:23, Ananyev, Konstantin:
> > 
> > 2016-03-09 13:36, Ananyev, Konstantin:
> > > > > +   if (to_send == 0)
> > > > > +           return 0;
> > > >
> > > > Why this check is done in the lib?
> > > > What is the performance gain if we are idle?
> > > > It can be done outside if needed.
> > >
> > > Yes, that could be done outside, but if user has to do it anyway,
> > > why not to put it inside?
> > > I don't expect any performance gain/loss because of that -
> > > just seems a bit more convenient to the user.
> > 
> > It is handling an idle case so there is no gain obviously.
> > But the condition branching is surely a loss.
> 
> I suppose that condition should always be checked:
> either in user code prior to function call or inside the
> function call itself.
> So don't expect any difference in performance here...
> Do you have any particular example when you think it would? 
> Or are you talking about rte_eth_tx_buffer() calling
> rte_eth_tx_buffer_flush() internally?
> For that one - both are flush is 'static inline' , so I expect
> compiler be smart enough to remove this redundant check.  
> 
> > So why the user would you like to do this check?
> Just for user convenience - to save him doing that manually.

Probably I've missed something. If we remove this check, the function
will do nothing, right? How is it changing the behaviour?