Re: [dpdk-dev] [PATCH v2] net/af_packet: fix ignoring full ring on tx
flat view
From: Ferruh Yigit <hidden>
Date: 2021-09-20 17:44:30
On 9/13/2021 2:45 PM, Tudor Cornea wrote:
quoted hunk ↗ jump to hunk
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 <redacted> Signed-off-by: Tudor Cornea <redacted> --- 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);