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

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Message-ID: <b16f0738-9b73-46f4-93ba-edcf84eb961a@nvidia.com>
Date: Wed, 30 Jul 2025 08:39:25 +0300
From: Gal Pressman <gal@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>,
 Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: Andrew Lunn <andrew@...n.ch>, Michael Chan <michael.chan@...adcom.com>,
 Pavan Chebbi <pavan.chebbi@...adcom.com>, Tariq Toukan <tariqt@...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 4:51, 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?

Exactly. mlx5 will use (0, 0) for sure.

> 
> 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;

Yes, that is a valid approach.