Jakub Kicinski wrote:
On Sun, 30 Nov 2025 09:56:24 -0500 Willem de Bruijn wrote:
Jakub Kicinski wrote:
On Fri, 28 Nov 2025 15:42:40 -0500 Willem de Bruijn wrote:
So GRO off disables HW_GRO, but not LRO? That difference is behavior is confusing. Could we still see this as a regression and make the ethtool HW_GRO feature equally independent from SW_GRO?
I couldn't convince myself that it's justified. Of course it would have made testing a lot easier. But apart from that - what's your reading of the status quo? Working backwards from were we ended up (and I haven't dug into the git history) I'm guessing that LRO disable is used to prevent changing geometry of the packets. GRO would presumably be disabled when user knows that it will be ineffective, to save the cost. Or when some portion of the stack (XDP?) can't deal with super frames.
If those are the reasons, practically, I don't see why user would want HW GRO without SW. Ever since we allowed SW GRO to re-GRO HW GRO'ed frames it's always better to leave SW enabled. HW leaves a lot of aggregation opportunities on the table.
I concluded that changing the current behavior would not help any real life scenario, just testing. LMK if you see one or the inconsistency is a big enough reason.
I think that's fair.
But from reading the code I don't see how disabling NETIF_F_GRO also disables NETIF_F_GRO_HW. And indeed I just tested on one (admittedly not latest upstream) IDPF driver and it does not.
Looks like you're right. Broadcom drivers where GRO_HW originates do it locally, so does qede. I guess somewhere along the way drives started treating GRO_HW as a separate feature rather than a GRO offload.
I don't think it changes the reasoning in any major way?
Agreed. If respinning, maybe change the wording a bit:
+ # a dummy XDP generic program. Disabling SW GRO as a feature -+ # would also disable HW GRO. ++ # may also disable HW GRO on some devices.