On Mon, 2 Oct 2017 18:02:46 -0700
Alexei Starovoitov <alexei.starovoi...@gmail.com> wrote:
> On Mon, Oct 02, 2017 at 06:05:29PM +0200, Jesper Dangaard Brouer wrote:
> > + while ((xdp_pkt = __ptr_ring_consume(rcpu->queue))) {
> > + struct sk_buff *skb;
> > + int ret;
> > +
> > + /* Allow busy polling again */
> > + empty_cnt = 0;
> > +
> > + skb = cpu_map_build_skb(rcpu, xdp_pkt);
> > + if (!skb) {
> > + page_frag_free(xdp_pkt);
> > + continue;
> > + }
> > +
> > + /* Inject into network stack */
> > + ret = netif_receive_skb(skb);
> > + if (ret == NET_RX_DROP)
> > + drops++;
>
> I thought the whole thing is an alternative to RPS,
> but netif_receive_skb_internal() will call into RPS logic.
> So the user has to make sure it disabled or they will
> conflict in some weird way?
In this patchset, cpumap and RPS are independent, and there is nothing
wrong with running RPS after cpumap have placed the SKB on a CPU.
Combining the two does seem a little weird. Especially since cpumap
doesn't (yet) transfer the HW-rxhash, thus extra SW-rxhash work will be
done by RPS.
I like you ABI argument. While combining RPS+cpumap is technically
possible, there isn't a good use-case for this. Thus, we should not
open this possibility, as we would need to support this combination
forever.
> Or you're calling netif_receive_skb() to be able to call
> generic XDP on that cpu again ?
That should not (currently) be possible. AFAIK we (Daniel) choose to
not allow Native and Generic XDP to be loaded on the same net_device.
(With the same ABI argument as here)
> But that prog can do cpumap redirect again?
> sort-of recursive redirect? Is it really useful?
> May be call into __netif_receive_skb_core() directly?
> not sure.
I like the idea of calling __netif_receive_skb_core() directly. I'll
send a V4 (after running my different benchmarks).
> I'm asking all these questions to make sure we think through
> these implications before it becomes an abi.
I fully follow your ABI argument. Thank you for bringing this up!
Do notice, that I expect to change this code path (later), to support
GRO. But it would be beneficial to get the HW-rxhash working first, as
it will speedup the GRO "same_flow" check, and allow cpumap to
distribute packets better.
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
