On 13/01/2026 13:04, Kenta Akagi wrote:

On 2026/01/13 15:43, Tariq Toukan wrote:

quoted

On 13/01/2026 8:31, Tariq Toukan wrote:

quoted

On 12/01/2026 9:03, Kenta Akagi wrote:

quoted

Hi,

I would like to measure the cable BER on ConnectX.

According to the documentation[1][2], there are counters that can be used
for this purpose: rx_corrected_bits_phy, rx_pcs_symbol_err_phy and
rx_bits_phy. However, rx_bits_phy does not show up in ethtool
statistics.

This patch exposes the PPCNT phy_received_bits as rx_bits_phy.


On a ConnectX-5 with 25Gbase connection, it works as expected.

On the other hand, although I have not verified it, in an 800Gbps
environment rx_bits_phy would likely overflow after about 124 days.
Since I cannot judge whether this is acceptable, I am posting this as an
RFC first.

Hi,

This is a 64-bits counter so no overflow is expected.

Sorry, ignore my comment, your numbers make sense.
Maybe it's ~248 days, but same idea.

Hi, thank you for checking.

Ah, it seems I didn't realize it was unsigned, and I also forgot to
include the expression. Sorry about that.
Yes - at 800 Gbps, 0xFFFFFFFFFFFFFFFF / (800 * (2^30) * 86400) = 248.55 days,
so it will overflow.

In practice, is it possible to expose this as a statistic via ethtool?
Or is there some other value that could be exposed for BER calculation - e.g.,
a register that indicates the elapsed seconds since link-up?

Thanks.

Hi Kenta,

You will find "FEC histogram" feature useful.
It splits the errors into ranges (bins), and plots a counter for each bin.
There's also a bin for 0-errors, which is what you're looking for.

Example output:

# ./tools/net/ynl/pyynl/cli.py --spec 
Documentation/netlink/specs/ethtool.yaml --do fec-get --json 
'{"header":{"dev-index": 5, "flags": 4}}'
{'active': 50,
'auto': 1,
'header': {'dev-index': 5, 'dev-name': 'eth3'},
'modes': {'bits': {}, 'nomask': True, 'size': 125},
'stats': {'corr-bits': [2810],
            'corrected': [2123],
            'hist': [{'bin-high': 0, 'bin-low': 0, 'bin-val': 235826196705},
                     {'bin-high': 1, 'bin-low': 1, 'bin-val': 1436},
                     {'bin-high': 2, 'bin-low': 2, 'bin-val': 687},
                     {'bin-high': 3, 'bin-low': 3, 'bin-val': 0},
                     {'bin-high': 4, 'bin-low': 4, 'bin-val': 0},
                     {'bin-high': 5, 'bin-low': 5, 'bin-val': 0},
                     {'bin-high': 6, 'bin-low': 6, 'bin-val': 0},
                     {'bin-high': 7, 'bin-low': 7, 'bin-val': 0},
                     {'bin-high': 8, 'bin-low': 8, 'bin-val': 0},
                     {'bin-high': 9, 'bin-low': 9, 'bin-val': 0},
                     {'bin-high': 10, 'bin-low': 10, 'bin-val': 0},
                     {'bin-high': 11, 'bin-low': 11, 'bin-val': 0},
                     {'bin-high': 12, 'bin-low': 12, 'bin-val': 0},
                     {'bin-high': 13, 'bin-low': 13, 'bin-val': 0},
                     {'bin-high': 14, 'bin-low': 14, 'bin-val': 0},
                     {'bin-high': 15, 'bin-low': 15, 'bin-val': 0}],
            'uncorr': [0]}}