On Mon, Sep 23, 2019 at 05:19:27PM +0100, Ray Kinsella wrote: > Hi folks, > > The ABI Stability proposals should be pretty well known at this point. > The latest rev is here ... > > http://inbox.dpdk.org/dev/1565864619-17206-1-git-send-email-...@ashroe.eu/ > > As has been discussed public data structure's are risky for ABI > stability, as any changes to a data structure can change the ABI. As a > general rule you want to expose as few as possible (ideally none), and > keep them as small as possible. > > One of the key data structures in DPDK is `struct rte_eth_dev`. In this > case, rte_eth_dev is exposed public-ally, as a side-effect of the > inlining of the [rx,tx]_burst functions. > > Marcin Zapolski has been looking at what to do about it, with no current > consensus on a path forward. The options on our table is:- > > 1. Do nothing, live with the risk to DPDK v20 ABI stability. > > 2. Pad rte_eth_dev, add some extra bytes to the structure "in case" we > need to add a field during the v20 ABI (through to 20.11). > > 3. Break rte_eth_dev into public and private structs. > - See > http://inbox.dpdk.org/dev/20190906131813.1343-1-marcinx.a.zapol...@intel.com/ > - This ends up quiet an invasive patch, late in the cycle, however it > does have no performance penalty. > > 4. Uninline [rx,tx]_burst functions > - See > http://inbox.dpdk.org/dev/20190730124950.1293-1-marcinx.a.zapol...@intel.com/ > - This has a performance penalty of ~2% with testpmd, impact on a "real > workload" is likely to be in the noise. > > We need to agree an approach for v19.11, and that may be we agree to do > nothing. My personal vote is 4. as the simplest with minimal impact. > Thanks for calling out these potential options, Ray.
#4, uninlining, would also be my preference, though I think #1, do nothing, is probably ok and could live with #2, adding padding, if others like the idea. While #3, splitting structures, has advantages, I just dislike how invasive it is, and don't think it's a good candidate for 19.11. /Bruce
