Re: [PATCH net-next 3/5] net: ethtool: add KUnit tests for the generated RSS key

On Mon, Sep 21, 2026 at 10:03 PM Jakub Kicinski [off-list ref] wrote:

On Mon, 21 Sep 2026 18:37:56 +0000 Eric Dumazet wrote:

quoted

Check the property from the definition of the Toeplitz hash, independently
of the way netdev_rss_key_init() achieves it: an aligned block of 2^q
consecutive values of one field has to land on the 2^q queues exactly once
each.

Four checks and a control. rss_key_property_test() does the algebra for
the named fields of the usual hash inputs, rss_key_grid_test() sweeps every
16-bit aligned position of the key, since the generator does not get to
know the layout the hardware uses, and rss_key_spread_test() hashes the
inputs of an actual burst and looks at where they land. The control,
rss_key_checker_test(), feeds degenerate keys to the rank check so that a
check accepting everything cannot make the others pass.

rss_key_alias_test() covers the other half of what the generator promises,
that no two input bits read the same 32-bit key window and are therefore
indistinguishable to the hash. It sorts the windows instead of comparing
them pairwise, so unlike netdev_rss_key_init() it looks at every distance
rather than at the multiples of 16 alone.

The field table includes a PSP over UDP over IPv6 layout, whose inner TCP
ports sit far past the plain 4-tuple, because that is the case the offsets
of the standard layouts do not cover.

Commenting out the fixup makes three of the five cases fail and leaves the
control passing. Keeping the fixup but skipping the redraw fails
rss_key_alias_test alone.

Is this AI generated or do you think there's some genuine value here?
I don't want kunits which can be trivially re-generated during
development to be merged. But perhaps there's some genuine value in
this one?

I added all these tests because Willem wanted them in our internal bug entry :)

This can certainly be removed, although I have to find ways to launch
vng so that
/proc/sys/net/core/netdev_rss_key is populated.