On Mon, Jun 24, 2019 at 2:51 AM Magnus Karlsson
<magnus.karlsson@xxxxxxxxx> wrote:
>
> On Sat, 15 Jun 2019 at 01:25, William Tu <u9012063@xxxxxxxxx> wrote:
> >
> > Hi,
> >
> > In my implementation[1], I'm doing s.t like
> > tx_done = xsk_ring_cons__peek(&xsk->umem->cq, BATCH_SIZE, &idx_cq);
> > if (tx_done > 0) {
> > xsk_ring_cons__release(&xsk->umem->cq, tx_done);
> > xsk->outstanding_tx -= tx_done;
> > }
> >
> > I expect if tx_done returns 32, then after calling xsk_ring_cons__release,
> > the next time I call xsk_ring_cons__peek, I should get idx_cq + 32.
> > However, sometimes I see the same value of idx_cq is returned as previous, even
> > when tx_done > 0. Is this the expected behavior?
> >
> > I experiment with xdpsock_user.c with the patch below and run
> > ~/bpf-next/samples/bpf# ./xdpsock -l -N -z -i eth3
> > using bpf-next commit 5e2ac390fbd08b2a462db66cef2663e4db0d5191
> >
> > --- a/samples/bpf/xdpsock_user.c
> > +++ b/samples/bpf/xdpsock_user.c
> > @@ -444,6 +443,8 @@ static void kick_tx(struct xsk_socket_info *xsk)
> > exit_with_error(errno);
> > }
> >
> > +static int prev_idx_cq;
> > +
> > static inline void complete_tx_l2fwd(struct xsk_socket_info *xsk)
> > {
> > u32 idx_cq = 0, idx_fq = 0;
> > @@ -463,6 +464,15 @@ static inline void complete_tx_l2fwd(struct
> > xsk_socket_info *xsk)
> > unsigned int i;
> > int ret;
> >
> > + if (idx_cq == prev_idx_cq) {
> > + printf("\n\n ERROR \n\n");
> > + }
> > + if (idx_cq - prev_idx_cq != rcvd) {
>
> William,
>
> You need to compare with prev_rcvd (and introduce that variable) here
> as the difference in index should be the same as the amount you
> received last time. If you do this change, you will get no errors. You
> can also see this pattern in your printouts. The diff is always equal
> to rcvd during the previous iteration.
>
> /Magnus
>
Hi Magnus,
Thanks for the clarification! Now I understand it's my mistake.
So:
rcvd1 = xsk_ring_cons__peek(&xsk->umem->cq, ndescs, &idx1_cq);
...
rcvd2 = xsk_ring_cons__peek(&xsk->umem->cq, ndescs, &idx2_cq);
and idx2_cq - idx1_cq == rcvd1.
--William
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