Fixed Ilya address. On Thu, Sep 26, 2019 at 1:50 PM David Marchand <david.march...@redhat.com> wrote: > > On Thu, Sep 26, 2019 at 1:13 PM Andrew Rybchenko > <arybche...@solarflare.com> wrote: > > > > On 9/24/19 7:50 PM, Ananyev, Konstantin wrote: > > > > Hi everyone, > > > > 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. > > > > My preference NOT to do #4. Reasons are: > > - I have seen performance drop from 1.5% to 3.5% based on the arm64 > > cores in use(Embedded vs Server cores) > > - We need the correct approach to cater to cryptodev and eventdev as > > well. If #4 is checked in, We will > > take shotcut for cryptodev and eventdev > > > > My preference #1, do nothing, is probably ok and could live with #2, > > adding padding, > > and fix properly with #3 as when needed and use #3 scheme for crypto > > dev and eventdev as well. > > > > > > My preference would be #4 also. > > If that's not an option, then I suppose #1 for 19.11 and #3 for next release > > when ABI breakage would be allowed. > > BTW, good point that we need similar thing for other dev types too. > > Konstantin > > > > > > My preference would be #4 or #1. > > #2 and #3 are both tradeoffs and do not resolve ABI breaking completely. > > #3 is really invasive, it requires changes of driverRx/Tx burst prototypes > > and > > uninline descriptor status functions (may be it would be better to change > > callback prototypes as well, but keep functions inline). > > #4 is better since it is really a step to ABI stability and it still allow > > to > > do many generic checks (dev->data dependent) on ethdev API level. > > Did we ensure that external users have all the required api before > hiding the rte_eth_dev struct? > ovs still accesses rte_eth_devices[]. > > CC Ian and Ilya.
-- David Marchand
