<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'? > > > > Rejected. > > > > There is no need for this modification now, and no actual use cases > > for it in the road map. In other words: This modification has no use cases; > > it > is purely academic. Many other suggestions have been rejected for the reason > that they have no current use cases. > > > > As Thomas mentioned, DPDK has transitioned towards being a library, > > rather than a pool of code to cherry-pick from. I have learned to live with > this. > > > > Being a library doesn't mean that functions cannot be exposed as > > inline code in the library header files. DPDK is mainly a high > > performance library with a tradition of exposing many of its internals in > > its > API, and we should keep it this way. We certainly don't want an opaque API > hiding all of its internals, passing around void pointers. > > > > However, it was still an interesting experiment to investigate the > performance cost. > > Yes, please reject it. I just tried to mark it rejected in patchwork, I do not have the permissions (probably you are the owner of the patch). Can you please mark it?
> Konstantin >
