From: Jakub Kicinski
> Sent: 17 May 2017 18:37
..
> > > while (todo--) {
> > > idx = D_IDX(tx_ring, tx_ring->rd_p++);
> >
> > That '++' looks suspicious.
> > I think you need to decide whether you are incrementing pointers into the
> > ring
> > or indexes into it.
> > Sometimes it is safer to use a non-wrapping index and mask when accessing
> > the entry.
> > entry_ptr = &ring[idx & (RING_SIZE - 1)]
> > Ring full is then (read_idx == write_idx + RING_SIZE),
> > ring empty (read_idx == write_idx).
> > So the index just wrap at (probably)_2^32.
>
> I may be missing the point. I use a mix of the two, actually, the
> software pointers are free running (non-wrapping) but the HW QCP
> pointers wrap. Because HW pointers wrap I always keep one entry on
> the rings empty, see nfp_net_tx_full().
Ah, I'd assumed that rd_p was a pointer, not an index.
David
