The number of Rx packets is computed as the sum of the unicast,
multicast and broadcast packet counters, minus the discarded packet
count:
ipackets = rx_unicast + rx_multicast + rx_broadcast - rx_discards
The unicast, multicast and broadcast counters already include the
packets that were subsequently dropped, so subtracting rx_discards
yields only the packets delivered to the application. These values are
provided by the PF in a virtchnl_eth_stats message; the PF samples them
from separate sources and the VF cannot guarantee the order in which
they are read. Under load, rx_discards can therefore momentarily exceed
the sum of the unicast, multicast and broadcast counters. As ipackets is
unsigned, the subtraction then wraps to a huge bogus value, reported to
the application as an enormous Rx packet count and packet rate.
The read order cannot be guaranteed from the VF, so use a saturating
subtraction: when rx_discards exceeds the sum of the unicast, multicast
and broadcast counters essentially nothing was delivered, so report zero
instead of underflowing.
Fixes: e71ffcc1008e ("net/iavf: fix Rx total stats")
Cc: [email protected]
Signed-off-by: Ciara Loftus <[email protected]>
---
drivers/net/intel/iavf/iavf_ethdev.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/drivers/net/intel/iavf/iavf_ethdev.c
b/drivers/net/intel/iavf/iavf_ethdev.c
index ec1ad02826..f2b100e290 100644
--- a/drivers/net/intel/iavf/iavf_ethdev.c
+++ b/drivers/net/intel/iavf/iavf_ethdev.c
@@ -1887,8 +1887,16 @@ iavf_dev_stats_get(struct rte_eth_dev *dev, struct
rte_eth_stats *stats,
RTE_ETH_RX_OFFLOAD_KEEP_CRC) ? 0 :
RTE_ETHER_CRC_LEN;
iavf_update_stats(vsi, &pstats);
- stats->ipackets = pstats.rx_unicast + pstats.rx_multicast +
- pstats.rx_broadcast - pstats.rx_discards;
+ stats->ipackets = pstats.rx_unicast + pstats.rx_multicast +
pstats.rx_broadcast;
+ /*
+ * Unicast/multicast/broadcast counters include discarded
packets, so subtract
+ * rx_discards to report only the packets delivered to the
application. The
+ * counters are sampled from separate sources and can be
momentarily inconsistent
+ * under load. If rx_discards exceeds their sum then
essentially nothing was
+ * delivered, so saturate at zero rather than underflow.
+ */
+ stats->ipackets = stats->ipackets >= pstats.rx_discards ?
+ stats->ipackets - pstats.rx_discards :
0;
stats->opackets = pstats.tx_broadcast + pstats.tx_multicast +
pstats.tx_unicast;
stats->imissed = pstats.rx_discards;
--
2.43.0
