Re: [PATCH v6 net-next 3/4] net: ena: Add PHC documentation

[Jakub Kicinski <kuba@kernel.org>]

On Mon, 10 Feb 2025 15:28:19 +0000 Arinzon, David wrote:
> You are right in the regard that it is not a network specific functionality.
> Having said that, PHC is a network card capability, making it a network-related component rather than purely a timekeeping feature.
> Moreover we failed to find an existing tool which would allow users to get valuable feedback of the system's overall health.
> 
> Researching its existing support in the kernel we noted that:
> - PHC is embedded in network NIC and is supported by multiple NIC vendors in the kernel
> - PHC information is visible through ethtool -T
> - The Linux networking stack uses PHC for timekeeping as well as for packet timestamping (via SO_TIMESTAMPING).
>   Packet timestamping statistics are available through ethtool get_ts_stats hook
> 
> We have found `ethtool -S` as a suitable location for exposing these statistics, which are unique to the ENA NIC.
> 
> We'd appreciate your thoughts on the matter, is there an alternative tool you can recommend?

We try to steer folks towards read-only debugfs files for stuff
that's not strictly networking related. You also add a custom
sysfs file in patch 4, I reckon adding stats there may also be
a natural place for the user? 

Patch 4 FWIW is lacking slightly in the justification, would 
be good to clarify why it's disabled by default. Single sentence
of "why" would be great.