Hi Ferruh, What you described above looks like a ring buffer with single producer and > single consumer, and producer overwrites the not consumed items.
Indeed. This is also my understanding of the bug. I am going to try to isolate the issue, and should probably be able to come up with a script in a few days. Our of curiosity, are you using an modified af_packet implementation in > kernel > for above described usage? We are currently using an Ubuntu-based distro with a 4.15 Linux kernel. We don't have any kernel patches for the af_packet implementation to my knowledge (probably excepting patches that are back-ported by Ubuntu maintainers from newer releases). On Mon, 20 Sept 2021 at 20:44, Ferruh Yigit <ferruh.yi...@intel.com> wrote: > On 9/13/2021 2:45 PM, Tudor Cornea wrote: > > The poll call can return POLLERR which is ignored, or it can return > > POLLOUT, even if there are no free frames in the mmap-ed area. > > > > We can account for both of these cases by re-checking if the next > > frame is empty before writing into it. > > > > Signed-off-by: Mihai Pogonaru <pogonarumi...@gmail.com> > > Signed-off-by: Tudor Cornea <tudor.cor...@gmail.com> > > --- > > drivers/net/af_packet/rte_eth_af_packet.c | 19 +++++++++++++++++++ > > 1 file changed, 19 insertions(+) > > > > diff --git a/drivers/net/af_packet/rte_eth_af_packet.c > b/drivers/net/af_packet/rte_eth_af_packet.c > > index b73b211..087c196 100644 > > --- a/drivers/net/af_packet/rte_eth_af_packet.c > > +++ b/drivers/net/af_packet/rte_eth_af_packet.c > > @@ -216,6 +216,25 @@ eth_af_packet_tx(void *queue, struct rte_mbuf > **bufs, uint16_t nb_pkts) > > (poll(&pfd, 1, -1) < 0)) > > break; > > > > + /* > > + * Poll can return POLLERR if the interface is down > > + * > > + * It will almost always return POLLOUT, even if there > > + * are no extra buffers available > > + * > > + * This happens, because packet_poll() calls > datagram_poll() > > + * which checks the space left in the socket buffer and, > > + * in the case of packet_mmap, the default socket buffer > length > > + * doesn't match the requested size for the tx_ring. > > + * As such, there is almost always space left in socket > buffer, > > + * which doesn't seem to be correlated to the requested > size > > + * for the tx_ring in packet_mmap. > > + * > > + * This results in poll() returning POLLOUT. > > + */ > > + if (ppd->tp_status != TP_STATUS_AVAILABLE) > > + break; > > + > > If 'POLLOUT' doesn't indicate that there is space in the buffer, what is > the > point of the 'poll()' at all? > > What can we test/reproduce the mentioned behavior? Or is there a way to > fix the > behavior of poll() or use an alternative of it? > > > OK to break on the 'POLLERR', I guess it can be detected in the > 'pfd.revent'. > > > > /* copy the tx frame data */ > > pbuf = (uint8_t *) ppd + TPACKET2_HDRLEN - > > sizeof(struct sockaddr_ll); > > > >
