Hangbin Liu <liuhangbin@xxxxxxxxx> writes: > On Fri, Jan 22, 2021 at 02:38:40PM +0100, Toke Høiland-Jørgensen wrote: >> >> out: >> >> + drops = cnt - sent; >> >> bq->count = 0; >> >> >> >> trace_xdp_devmap_xmit(bq->dev_rx, dev, sent, drops, err); >> >> bq->dev_rx = NULL; >> >> + bq->xdp_prog = NULL; >> > >> > One more question, do you really have to do that per each bq_xmit_all >> > call? Couldn't you clear it in __dev_flush ? >> > >> > Or IOW - what's the rationale behind storing xdp_prog in >> > xdp_dev_bulk_queue. Why can't you propagate the dst->xdp_prog and rely on >> > that without that local pointer? >> > >> > You probably have an answer for that, so maybe include it in commit >> > message. >> > >> > BTW same question for clearing dev_rx. To me this will be the same for all >> > bq_xmit_all() calls that will happen within same napi. >> >> I think you're right: When bq_xmit_all() is called from bq_enqueue(), >> another packet will always be enqueued immediately after, so clearing >> out all of those things in bq_xmit_all() is redundant. This also >> includes the list_del on bq->flush_node, BTW. >> >> And while we're getting into e micro-optimisations: In bq_enqueue() we >> have two checks: >> >> if (!bq->dev_rx) >> bq->dev_rx = dev_rx; >> >> bq->q[bq->count++] = xdpf; >> >> if (!bq->flush_node.prev) >> list_add(&bq->flush_node, flush_list); >> >> >> those two if() checks can be collapsed into one, since the list and the >> dev_rx field are only ever modified together. This will also be the case >> for bq->xdp_prog, so putting all three under the same check in >> bq_enqueue() and only clearing them in __dev_flush() would be a win, I >> suppose - nice catch! :) > > Thanks for the advice, so how about modify it like: Yup, exactly! :) -Toke
