Re: [PATCH net-next v2 2/3] net: dsa: add Arrow SpeedChips XRS700x driver

On Fri, 27 Nov 2020 21:47:14 +0100 Andrew Lunn wrote:

quoted

Is the periodic refresh really that awful? We're mostly talking error
counters here so every second or every few seconds should be perfectly
fine.  

Humm, i would prefer error counts to be more correct than anything
else. When debugging issues, you generally don't care how many packets
worked. It is how many failed you are interesting, and how that number
of failures increases.

Right, but not sure I'd use the word "correct". Perhaps "immediately up
to date"?

High speed NICs usually go through a layer of firmware before they
access the stats, IOW even if we always synchronously ask for the stats
in the kernel - in practice a lot of NICs (most?) will return some form
of cached information.

So long as these counters are still in ethtool -S, i guess it does not
matter. That i do trust to be accurate, and probably consistent across
the counters it returns.

Not in the NIC designs I'm familiar with.

But anyway - this only matters in some strict testing harness, right?
Normal users will look at a stats after they noticed issues (so minutes
/ hours later) or at the very best they'll look at a graph, which will
hardly require <1sec accuracy to when error occurred.