13/10/2020 14:29, Bing Zhao:
> From: Thomas Monjalon <tho...@monjalon.net>
> > 08/10/2020 14:05, Bing Zhao:
> > > struct rte_eth_hairpin_conf {
> > > - uint16_t peer_count; /**< The number of peers. */
> > > + uint32_t peer_count:16; /**< The number of peers. */
> >
> > Why not keeping uint16_t?
>
> The inside structure has a multiple of 4B, and the peer_count now only takes
> about 2B. AFAIK, usually, the structure will have an aligned length/offset
> and there will be some padding between the 2B + (2B pad) + 4B * 32 or 2B +
> (2B +2B) * 32 + 2B, depending on the compiler.
> I changed to bit fields of a u32 due to the two facts:
> 1. Using the 2B and keep the whole structure aligned. No waste except the
> reserved bits.
> 2. Only u32 with bit fields is standard.
Oh I see, this is because u16 bit fields are not standard?
> > > + uint32_t tx_explicit:1; /**< Explicit TX flow rule mode. */
> > > + uint32_t manual_bind:1; /**< Manually bind hairpin queues.
> > */
> >
> > Please describe more the expectations of these bits:
> > What is changed at ethdev or PMD level?
>
> In ethdev level, there is almost no change. This attribute will be passed to
> PMD directly through the function pointer.
> In PMD level, these bits should be checked and better to be saved. And the
> attribute fields should be checked for per queue pair and all the queues, and
> each queue pair should have the same attributes configured to make the
> behavior aligned. But it depends on the PMD itself to decide if all the queue
> pairs between a port pair should have the same attributes, or even all the
> queues from / to same port of all hairpin port pairs.
> If manual_bind is not set, then the PMD will try to bind the queues and
> enable hairpin during device start stage and there is no need to call the
> bind / unbind API.
> If tx_explicit is set, the application should insert the RX flow rules and TX
> flow rules seperataly and connect the RX/TX logic connection together.
>
> > What the application is supposed to do?
>
> The application should specify the new two attributes during the queue setup.
> And also, it could leave it unset (0 by default) to keep the behavior
> compatible with the previous release.
> If manual_bind is set, then it is the application's responsibility to call
> the bind / unbind API to enable / disable the hairpin between specific ports.
> If tx_explicit is set, as described above, the application should maintain
> the flows logic to make hairpin work as expected, e.g., they can choose
> metadata (not the only method), in the RX flow, the metadata is set and in
> the TX flow, it is used for matching. Then even if the headers are changed
> with NAT action or encap, the hairpin function could work as expected.
>
> > Why choosing one mode or the other?
>
> If the application wants to have the full control of hairpin flows, it could
> chose the explicit TX flow mode.
> If two or more ports involved into the hairpin, it is suggested to use the
> manual bind.
> Please note, the actual supported attributes denpend on the PMD and HW.
The application impact must be described shortly in doxygen please.
