mlxsw: spectrum_ethtool: expose per-PG rx_discards

PPCNT group 0x10 (per-priority counters) carries an rx_discards field at
offset 0x78. These counters aggregate up into if_in_discards, but don't
show up anywhere else. Since there are many things that aggregate into
`if_in_discards`, having these counters helps distinguish what caused
those discards (in my case they were caused by headroom buffer overruns
due to inappropriately configured buffer sizes).

Of note, from emperical testing, these counter are per-"priority group"
(PG) not per-"switch priority". It's a bit confusing, because the rest
of these counter are per-"switch priority" and the header file calls
these "Per Priority Group Counters". However, that should be read as
"(Per Priority) Group Counters", not "Per (Priority Group) Counters".

I attempted to distinguish this in the counter naming by calling these
`rx_discards_pg_N` rather than `rx_discards_prio_N` (which is the
naming scheme of the other counters in this PPCNT group).

I will also note that the mlx5 driver (which already has this counter)
uses the schme `rx_prioN_discards` (and same for the other counters
in this group). However, I was unable to determine whether the mlx5
counters behave the same as the mlxsw counters with respect to PG
mapping. An attempt to remap to a different PG there did not change
which counter incremented, but the mlx5 configuration code is quite
different, so it's possible the remapping needs to be done differently.

Signed-off-by: Keno Fischer <keno@juliahub.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Link: https://patch.msgid.link/agqkMwgM1PdkyMUR@juliahub.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions