On Wed, Jun 29, 2022 at 2:58 PM Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx> wrote: > > On Wed, Jun 29, 2022 at 02:45:11PM +0200, Björn Töpel wrote: > > On Wed, 29 Jun 2022 at 12:58, Maciej Fijalkowski > > <maciej.fijalkowski@xxxxxxxxx> wrote: > > > > > > When application runs in zero copy busy poll mode and does not receive a > > > single packet but only sends them, it is currently impossible to get > > > into napi_busy_loop() as napi_id is only marked on Rx side in > > > xsk_rcv_check(). In there, napi_id is being taken from xdp_rxq_info > > > carried by xdp_buff. From Tx perspective, we do not have access to it. > > > What we have handy is the xsk pool. > > > > The fact that the napi_id is not set unless set from the ingress side > > is actually "by design". It's CONFIG_NET_RX_BUSY_POLL after all. I > > followed the semantics of the regular busy-polling sockets. So, I > > wouldn't say it's a fix! The busy-polling in sendmsg is really just > > about "driving the RX busy-polling from another socket syscall". > > I just felt that busy polling for txonly apps was broken, hence the > 'fixing' flavour. I can send it just as improvement to bpf-next. > > > > > That being said, I definitely see that this is useful for AF_XDP > > sockets, but keep in mind that it sort of changes the behavior from > > regular sockets. And we'll get different behavior for > > copy-mode/zero-copy mode. > > > > TL;DR, I think it's a good addition. One small nit below: > > > > > + __sk_mark_napi_id_once(sk, xs->pool->heads[0].xdp.rxq->napi_id); > > > > Please hide this hideous pointer chasing in something neater: > > xsk_pool_get_napi_id() or something. > > Would it make sense to introduce napi_id to xsk_buff_pool then? Only if it has a positive performance impact. Let us not carry copies of state otherwise. So please measure first and see if it makes any difference. If not, I prefer the pointer chasing hidden behind an API like Björn suggests. > xp_set_rxq_info() could be setting it. We are sure that napi_id is the > same for whole pool (each xdp_buff_xsk's rxq info). > > > > > > > Björn
