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

["Kulasek, TomaszX" <tomaszx.kulasek@intel.com>]

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> Sent: Wednesday, March 9, 2016 16:27
> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> Cc: Kulasek, TomaszX <tomaszx.kulasek@intel.com>; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2 1/2] ethdev: add buffered tx api
> 
> 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.

Tomasz