linux-kernel - Re: [PATCH RFC mlx5-next 0/1] net/mlx5e: Expose physical received bits counters to ethtool

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Message-ID: <ba9b732c-7c83-4837-9310-02b6a133169f@gmail.com>
Date: Wed, 28 Jan 2026 09:14:56 +0200
From: Tariq Toukan <ttoukan.linux@...il.com>
To: Kenta Akagi <k@...l.me>, saeedm@...dia.com, tariqt@...dia.com,
 mbloch@...dia.com, leon@...nel.org, andrew+netdev@...n.ch,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com
Cc: netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC mlx5-next 0/1] net/mlx5e: Expose physical received
 bits counters to ethtool



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]}}