On Mon, Dec 4, 2017 at 12:58 PM, Alexander Duyck
[off-list ref] wrote:

On Mon, Dec 4, 2017 at 11:52 AM, Michael Chan [off-list ref] wrote:

quoted

NETIF_F_GRO_HW is a flag that depends on NETIF_F_GRO.  In some ways,
it is similar to a private flag that depends on NETIF_F_LRO.  But I
think a standard flag is better.

Why would you make it dependent on NETIF_F_GRO? That doesn't make any
sense to me. It gets in the way of GRO anyway as it can't assemble an
already aggregated frame.

GRO_HW is basically hardware accelerated GRO.  If the user doesn't
want GRO at all (let's say he is running generic XDP, or he wants
tcpdump to show the packets on the wire), disabling GRO should disable
everything.  It's more intuitive that way.

It seems more like the two features should be able to co-exist with
either one being able to be disabled/enabled independently. It makes
it much easier to debug things this way. Otherwise there is no way to
tell if a given issue is software or hardware GRO since disabling
software disables them both.

quoted

quoted

quoted

quoted

I think I would rather have something like a netdev private flag that
says LRO assembled frames are routable and just have this all run over
the LRO flag with a test for the private flag to avoid triggering the
LRO disable in the case of the flag being present. Really this is just
a clean LRO implementation anyway so maybe we should just go that
route where LRO is the hardware offload and GRO is the generic
software implementation of that offload. That way when GRO gets some
new feature that your hardware doesn't support we don't have to argue
about the differences since LRO is meant to be a limited
implementation anyway due to the nature of it being in hardware.

Private flag will work.  But a standard feature flag is better since
there are multiple drivers supporting this.  A standard way to turn
this on/off is a better user experience.  It's also consistent with
TSO/GSO on the transmit side.

I agree, and that is why I would prefer to see this use the LRO flag.
It is the flag that is normally used to indicating Rx coalescing in
hardware. Coming up with a custom feature flag for a form of LRO that
your hardware does doesn't make much sense to me. Otherwise I might as
well go modify ixgbe and rename the LRO it does to GRO_HW since I can
make it do most of what you are doing here.

Again, there is enough difference between LRO and hardware GRO that it
makes sense to add a new flag.  Functionally, a private flag will work
too, but a standard flag makes more intuitive sense to me and to
users.

Yeah, the idea is that any vendor can use GRO_HW.  Today, there are 3
drivers supporting it.  I'm sure there will be other drivers
supporting this in the future.  For something that is supported by
multiple vendors, that's another reason to use a standard flag.

quoted

quoted

quoted

To me it just seems like this is an attempt to use the GRO name as a
marketing term and I really don't like the feel of it.

I disagree with this.  It's more than a marketing term.

Not really. It is a subset of GRO offload in hardware. In my mind that
is just LRO. I say subset since odds are you don't support all of the
same protocols and tunnels that GRO in software does.

Of course, hardware has some limitations, such as the number of TCP
connections it can aggregate, etc.  But again, it is different from
LRO.

The bit I don't like about this is that if you bond a device that is
running LRO with one that is running GSO_HW you now have to disable
two flags on the bond in order to disable hardware aggregation.

Admittedly I haven't take a look at the entire patch set, but did you
also take care of the flag sychronization issues this is going to
cause with upper devices such as vlan, macvlan, bond, etc?

I will take another look.  Thanks.