On 2019/05/23 20:11, Toke Høiland-Jørgensen wrote: > Toshiaki Makita <makita.toshiaki@xxxxxxxxxxxxx> writes: > >> XDP_TX is similar to XDP_REDIRECT as it essentially redirects packets to >> the device itself. XDP_REDIRECT has bulk transmit mechanism to avoid the >> heavy cost of indirect call but it also reduces lock acquisition on the >> destination device that needs locks like veth and tun. >> >> XDP_TX does not use indirect calls but drivers which require locks can >> benefit from the bulk transmit for XDP_TX as well. > > XDP_TX happens on the same device, so there's an implicit bulking > happening because of the NAPI cycle. So why is an additional mechanism > needed (in the general case)? Not sure what the implicit bulking you mention is. XDP_TX calls .ndo_xdp_xmit() for each packet, and it acquires a lock in veth and tun. To avoid this, we need additional storage for bulking like devmap for XDP_REDIRECT. -- Toshiaki Makita
