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.


[1] commit 8ce3b586faa4 ("net/mlx5: Add counter information to mlx5
    driver documentation")
[2] https://docs.kernel.org/networking/device_drivers/ethernet/mellanox/mlx5/counters.html

Kenta Akagi (1):
  net/mlx5e: Expose physical received bits counters to ethtool

 drivers/net/ethernet/mellanox/mlx5/core/en_stats.c | 1 +
 1 file changed, 1 insertion(+)

-- 
2.50.1

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

> 
> [1] commit 8ce3b586faa4 ("net/mlx5: Add counter information to mlx5
>      driver documentation")
> [2] https://docs.kernel.org/networking/device_drivers/ethernet/mellanox/mlx5/counters.html
> 
> Kenta Akagi (1):
>    net/mlx5e: Expose physical received bits counters to ethtool
> 
>   drivers/net/ethernet/mellanox/mlx5/core/en_stats.c | 1 +
>   1 file changed, 1 insertion(+)
>

On 13/01/2026 8:31, Tariq Toukan wrote:
> 
> 
> On 12/01/2026 9:03, Kenta Akagi wrote:
>> 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.

>>
>> [1] commit 8ce3b586faa4 ("net/mlx5: Add counter information to mlx5
>>      driver documentation")
>> [2] https://docs.kernel.org/networking/device_drivers/ethernet/ 
>> mellanox/mlx5/counters.html
>>
>> Kenta Akagi (1):
>>    net/mlx5e: Expose physical received bits counters to ethtool
>>
>>   drivers/net/ethernet/mellanox/mlx5/core/en_stats.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
> 

On 2026/01/13 15:43, Tariq Toukan wrote:
> 
> 
> On 13/01/2026 8:31, Tariq Toukan wrote:
>>
>>
>> On 12/01/2026 9:03, Kenta Akagi wrote:
>>> 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.

>>>
>>> [1] commit 8ce3b586faa4 ("net/mlx5: Add counter information to mlx5
>>>      driver documentation")
>>> [2] https://docs.kernel.org/networking/device_drivers/ethernet/ mellanox/mlx5/counters.html
>>>
>>> Kenta Akagi (1):
>>>    net/mlx5e: Expose physical received bits counters to ethtool
>>>
>>>   drivers/net/ethernet/mellanox/mlx5/core/en_stats.c | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>
> 
> 

On 13/01/2026 13:04, Kenta Akagi wrote:
> On 2026/01/13 15:43, Tariq Toukan wrote:
>>
>>
>> On 13/01/2026 8:31, Tariq Toukan wrote:
>>>
>>>
>>> On 12/01/2026 9:03, Kenta Akagi wrote:
>>>> 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]}}