15/06/2021 10:00, Jerin Jacob: > On Tue, Jun 15, 2021 at 12:22 PM Thomas Monjalon <tho...@monjalon.net> wrote: > > 14/06/2021 17:48, Jerin Jacob: > > > On Mon, Jun 14, 2021 at 8:29 PM Ananyev, Konstantin > > > <konstantin.anan...@intel.com> wrote: > > > > > 14/06/2021 15:15, Bruce Richardson: > > > > > > While I dislike the hard-coded limits in DPDK, I'm also not > > > > > > convinced that > > > > > > we should switch away from the flat arrays or that we need fully > > > > > > dynamic > > > > > > arrays that grow/shrink at runtime for ethdevs. I would suggest a > > > > > > half-way > > > > > > house here, where we keep the ethdevs as an array, but one > > > > > > allocated/sized > > > > > > at runtime rather than statically. This would allow us to have a > > > > > > compile-time default value, but, for use cases that need it, allow > > > > > > use of a > > > > > > flag e.g. "max-ethdevs" to change the size of the parameter given > > > > > > to the > > > > > > malloc call for the array. This max limit could then be provided > > > > > > to apps > > > > > > too if they want to match any array sizes. [Alternatively those > > > > > > apps could > > > > > > check the provided size and error out if the size has been > > > > > > increased beyond > > > > > > what the app is designed to use?]. There would be no extra > > > > > > dereferences per > > > > > > rx/tx burst call in this scenario so performance should be the same > > > > > > as > > > > > > before (potentially better if array is in hugepage memory, I > > > > > > suppose). > > > > > > > > > > I think we need some benchmarks to decide what is the best tradeoff. > > > > > I spent time on this implementation, but sorry I won't have time for > > > > > benchmarks. > > > > > Volunteers? > > > > > > > > I had only a quick look at your approach so far. > > > > But from what I can read, in MT environment your suggestion will require > > > > extra synchronization for each read-write access to such parray element > > > > (lock, rcu, ...). > > > > I think what Bruce suggests will be much ligther, easier to implement > > > > and less error prone. > > > > At least for rte_ethdevs[] and friends. > > > > > > +1 > > > > Please could you have a deeper look and tell me why we need more locks? > > We don't need more locks (It is fat mutex) now in the implementation. > > If it needs to use in fastpath, we need more state of art > synchronization like RCU. > > Also, you can take look at VPP dynamic array implementation which is > used in fastpath. > > https://docs.fd.io/vpp/21.10/db/d65/vec_8h.html > > So the question is the use case for this API. Is it for slowpath item > like ethdev[] memory > or fastpath items like holding an array of mbuf etc.
As I replied to Morten, it is for read in fast path and alloc/free in slow path. I should highlight this in the commit log if there is a v2. That's why there is a mutex in alloc/free and nothing in read access. > > The element pointers doesn't change. > > Only the array pointer change at resize, > > but the old one is still usable until the next resize. > > I think we don't need more.
