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

[Thomas Monjalon]

2016-03-09 15:32, Kulasek, TomaszX:
> From: Thomas Monjalon [mailto:thomas.monjalon at 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?
> 
> If we remove this check, function will try to send 0 packets and check
> condition for error. So we gain nothing with removing that.

Actually I should not arguing why removing it,
but you should arguing why adding it :)