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 order in which they are read cannot be
guaranteed. 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, 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: c9f889e99616 ("net/ice: enable stats for DCF")
Cc: [email protected]
Signed-off-by: Ciara Loftus <[email protected]>
---
drivers/net/intel/ice/ice_dcf_ethdev.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/drivers/net/intel/ice/ice_dcf_ethdev.c
b/drivers/net/intel/ice/ice_dcf_ethdev.c
index 4fce59617e..c78b290b0d 100644
--- a/drivers/net/intel/ice/ice_dcf_ethdev.c
+++ b/drivers/net/intel/ice/ice_dcf_ethdev.c
@@ -1523,8 +1523,16 @@ ice_dcf_stats_get(struct rte_eth_dev *dev, struct
rte_eth_stats *stats,
ret = ice_dcf_query_stats(hw, &pstats);
if (ret == 0) {
ice_dcf_update_stats(&hw->eth_stats_offset, &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
