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

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Message-ID: <20250729185146.513504e0@kernel.org>
Date: Tue, 29 Jul 2025 18:51:46 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: 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>,
 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 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?

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;