netdev - Re: [RFC PATCH] ethtool: add FEC bins histogramm report

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Message-ID: <bb66c931-ac17-4a70-ba11-2a109794b9e2@linux.dev>
Date: Wed, 30 Jul 2025 10:18:46 +0100
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Andrew Lunn <andrew@...n.ch>, Michael Chan <michael.chan@...adcom.com>,
 Pavan Chebbi <pavan.chebbi@...adcom.com>, Tariq Toukan <tariqt@...dia.com>,
 Gal Pressman <gal@...dia.com>, intel-wired-lan@...ts.osuosl.org,
 Donald Hunter <donald.hunter@...il.com>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>, netdev@...r.kernel.org
Subject: Re: [RFC PATCH] ethtool: add FEC bins histogramm report

On 30/07/2025 02:51, Jakub Kicinski wrote:
> On Tue, 29 Jul 2025 19:07:59 +0100 Vadim Fedorenko wrote:
>> On 29/07/2025 18:31, Andrew Lunn wrote:
>>>> The only one bin will have negative value is the one to signal the end
>>>> of the list of the bins, which is not actually put into netlink message.
>>>> It actually better to change spec to have unsigned values, I believe.
>>>
>>> Can any of these NICs send runt packets? Can any send packets without
>>> an ethernet header and FCS?
>>>
>>> Seems to me, the bin (0,0) is meaningless, so can could be considered
>>> the end marker. You then have unsigned everywhere, keeping it KISS.
>>
>> I had to revisit the 802.3df-2024, and it looks like you are right:
>> "FEC_codeword_error_bin_i, where i=1 to 15, are optional 32-bit
>> counters. While align_status is true, for each codeword received with
>> exactly i correctable 10-bit symbols"
>>
>> That means bin (0,0) doesn't exist according to standard, so we can use
>> it as a marker even though some vendors provide this bin as part of
>> histogram.
> 
> IDK, 0,0 means all symbols were completely correct.
> It may be useful for calculating bit error rate?

The standard doesn't have this bin, its value can be potentially
deducted from all packets counter.

> 
> A workaround for having the {-1, -1} sentinel could also be to skip
> the first entry:
> 
> 	if (i && !ranges[i].low && !ranges[i].high)
> 		break;

I was thinking of this way, the problem is that in the core we rely on
the driver to provide at least 2 bins and we cannot add any compile-time
checks because it's all dynamic.