<snip> > Subject: Re: [dpdk-dev] [RFC] ring: make ring implementation non-inlined > > 26/03/2020 09:04, Morten Brørup: > > From: Jerin Jacob > > > On Fri, Mar 20, 2020 Konstantin Ananyev wrote: > > > > > > > > As was discussed here: > > > > http://mails.dpdk.org/archives/dev/2020-February/158586.html > > > > this RFC aimed to hide ring internals into .c and make all ring > > > > functions non-inlined. In theory that might help to maintain ABI > > > > stability in future. > > > > This is just a POC to measure the impact of proposed idea, proper > > > > implementation would definetly need some extra effort. > > > > On IA box (SKX) ring_perf_autotest shows ~20-30 cycles extra for > > > > enqueue+dequeue pair. On some more realistic code, I suspect > > > > the impact it might be a bit higher. > > > > For MP/MC bulk transfers degradation seems quite small, though for > > > > SP/SC and/or small transfers it is more then noticable (see exact > > > > numbers below). > > > > From my perspective we'd probably keep it inlined for now to avoid > > > > any non-anticipated perfomance degradations. > > > > Though intersted to see perf results and opinions from other > > > > interested parties. > > > > > > +1 > > Konstantin, thank you for doing some measures > > > > > My reasoning is a bit different, DPDK is using in embedded boxes too > > > where performance has more weight than ABI stuff. > > > > As a network appliance vendor I can confirm that we certainly care > > more about performance than ABI stability. > > ABI stability is irrelevant for us; > > and API instability is a non-recurring engineering cost each time we > > choose to switch to a new DPDK version, which we only do if we cannot > > avoid it, e.g. due to new drivers, security fixes or new features that > > we want to use. > > > > For us, the trend pointed in the wrong direction when DPDK switched > > the preference towards runtime configurability and deprecated compile > > time configurability. I do understand the reasoning behind it, and the > > impact is minimal, so we accept it. > > The code can be optimized by removing some instructions with #ifdef. > But the complexity of managing #ifdef enabling/disabling, depending on the > platform and the use case, would be huge. > We try to have a reasonable code "always enabled" which performs well in all > cases. This is a design choice which makes DPDK a library, not a pool of code > to cherry-pick. > > > However, if DPDK starts sacrificing performance of the core libraries > > for the benefits of the GNU/Linux distributors, network appliance > > vendors may put more effort into sticking with old DPDK versions > > instead of updating. > > The initial choice regarding ABI compatibility was "do not care". > Recently, the decision was done to care about ABI compatibility as priority > number 2. The priority number 1 remains the performance. > That's a reason for allowing some ABI breakages in some specific releases > announced in advance. > > > > I think we need to focus first on slow path APIs ABI stuff. > > Yes we should not degrade fast path performance for the sake of avoiding > uncertain future ABI issues. > > Morten, Jerin, thank you for the feedback. I think we have a consensus here not to make any changes to inline functions for now. Should we mark this as 'Deferred or Rejected'?
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