https://bugs.dpdk.org/show_bug.cgi?id=409
Bug ID: 409
Summary: testpmd sometimes does not correctly show RX-missed on
Mellanox NICs
Product: DPDK
Version: 19.11
Hardware: All
OS: All
Status: UNCONFIRMED
Severity: normal
Priority: Normal
Component: testpmd
Assignee: dev@dpdk.org
Reporter: c...@hpe.com
Target Milestone: ---
When running testpmd using the Mellanox driver (mlx5), the value shown for
RX-missed will overflow and show an extremely large value at times. This
appears to occur when
/sys/devices/.../inifiband/mlx5_*/ports/*/hw_counters/out_of_buffer rolls over.
This value is an unsigned 32 bit and testpmd uses an unsigned 64 bit to store
the value. The initial value is read when testpmd is started, then a new value
is read while it is running. If the value read is less than the initial read
(after a rollover occurs), the difference will result in a negative value (or
in the case of unsigned storage, an extremely large value).
The calculation occurs in mlx5_stats_get():
mlx5_read_ib_stat(priv, "out_of_buffer", &tmp.imissed);
tmp.imissed -= priv->stats_ctrl.imissed_base;
Where the stored value, priv->stats_ctrl.imissed_base, contains a larger value
than the value stored in tmp.imissed.
Two possible solutions are to change the Mellanox drivers to use an unsigned 64
bit value for out_of_buffer in sysfs (so that it doesn't rollover), or to
modify the mlx5 code to account for the rollover.
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