On Mon, Oct 16, 2023 at 4:31 PM Jakub Kicinski [off-list ref] wrote:

On Mon, 16 Oct 2023 15:55:21 -0700 Alexander Duyck wrote:

quoted

It would make more sense to just add it as a variant hash function of
toeplitz. If you did it right you could probably make the formatting
pretty, something like:
RSS hash function:
    toeplitz: on
        symmetric xor: on
    xor: off
    crc32: off

It doesn't make sense to place it in the input flags and will just
cause quick congestion as things get added there. This is an algorithm
change so it makes more sense to place it there.

Algo is also a bit confusing, it's more like key pre-processing?
There's nothing toeplitz about xoring input fields. Works as well
for CRC32.. or XOR.

I agree that the change to the algorithm doesn't necessarily have
anything to do with toeplitz, however it is still a change to the
algorithm by performing the extra XOR on the inputs prior to
processing. That is why I figured it might make sense to just add a
new hfunc value that would mean toeplitz w/ symmetric XOR.

We can use one of the reserved fields of struct ethtool_rxfh to carry
this extension. I think I asked for this at some point, but there's
only so much repeated feedback one can send in a day :(

Why add an extra reserved field when this is just a variant on a hash
function? I view it as not being dissimilar to how we handle TSO or
tx-checksumming. It would make sense to me to just set something like
toeplitz-symmetric-xor to on in order to turn this on.