On Mon, Sep 28, 2020 at 11:25:34AM +0100, Ferruh Yigit wrote: > On 9/28/2020 8:31 AM, Dumitru Ceara wrote: > > On 9/22/20 4:21 PM, Ferruh Yigit wrote: > > > On 9/18/2020 11:36 AM, Dumitru Ceara wrote: > > > > Even though ring interfaces don't support any other TX/RX offloads they > > > > do support sending multi segment packets and this should be advertised > > > > in order to not break applications that use ring interfaces. > > > > > > > > > > Does ring PMD support sending multi segmented packets? > > > > > > > Yes, sending multi segmented packets works fine with ring PMD. > > > > Define "works fine" :) > > All PMDs can put the first mbuf of the chained mbuf to the ring, in that > case what is the difference between the ones supports > 'DEV_TX_OFFLOAD_MULTI_SEGS' and the ones doesn't support? > > If the traffic is only from ring PMD to ring PMD, you won't recognize the > difference between segmented or not-segmented mbufs, and it will look like > segmented packets works fine. > But if there is other PMDs involved in the forwarding, or if need to process > the packets, will it still work fine? >
What other PMDs do or don't do should be irrelevant here, I think. The fact that multi-segment PMDs make it though the ring PMD in valid form should be sufficient to mark it as supported. > > > As far as I can see ring PMD doesn't know about the mbuf segments. > > > > > > > Right, the PMD doesn't care about the mbuf segments but it implicitly > > supports sending multi segmented packets. From what I see it's actually > > the case for most of the PMDs, in the sense that most don't even check > > the DEV_TX_OFFLOAD_MULTI_SEGS flag and if the application sends multi > > segment packets they are just accepted. > > > > As far as I can see, if the segmented packets sent, the ring PMD will put > the first mbuf into the ring without doing anything specific to the next > segments. > > If the 'DEV_TX_OFFLOAD_MULTI_SEGS' is supported I expect it should detect > the segmented packets and put each chained mbuf into the separate field in > the ring. > Why, what would be the advantage of that? Right now if you send in a valid packet chain to the Ring PMD, you get a valid packet chain out again the other side, so I don't see what needs to change about that behaviour. > > > > However, the fact that the ring PMD doesn't advertise this implicit > > support forces applications that use ring PMD to have a special case for > > handling ring interfaces. If the ring PMD would advertise > > DEV_TX_OFFLOAD_MULTI_SEGS this would allow upper layers to be oblivious > > to the type of underlying interface. > > > > This is not handling the special case for the ring PMD, this is why he have > the offload capability flag. Application should behave according capability > flags, not per specific PMD. > > Is there any specific usecase you are trying to cover?
