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Date: Thu, 03 Dec 2020 22:35:12 +0100 From: Tobias Waldekranz <tobias@...dekranz.com> To: Andrew Lunn <andrew@...n.ch> Cc: Vladimir Oltean <olteanv@...il.com>, davem@...emloft.net, kuba@...nel.org, vivien.didelot@...il.com, f.fainelli@...il.com, j.vosburgh@...il.com, vfalico@...il.com, andy@...yhouse.net, netdev@...r.kernel.org Subject: Re: [PATCH v3 net-next 2/4] net: dsa: Link aggregation support On Thu, Dec 03, 2020 at 22:09, Andrew Lunn <andrew@...n.ch> wrote: >> One could argue that if Linus had received an error instead, adapted his >> teamd config and tried again, he would be a happier user and we might >> not have to compete with his OS. >> >> I am not sure which way is the correct one, but I do not think that it >> necessarily _always_ correct to silently fallback to a non-offloaded >> mode. > > This is an argument Mellanox makes, where falling back to software > would be a bad idea given the huge bandwidth of their hardware > accelerator, and the slow bandwidth of their CPU. Yeah when you have 100G interfaces the choice becomes easier :) > If the switch has no hardware support for LAG at all, then falling > back to software is reasonable. It is less clear when there is some > support in the switch. If we do reject it, we should try to make use > of extack to give the user a useful error messages: Not supported, try > configuration XYZ. But i guess that needs some plumbing, getting > extack available in the place we make the decision. I do not think we need to add anything. Looking at mlxsw, the extack is available in the `struct netdev_notifier_changeupper_info`. I am leaning towards the behavior you just described: - If there is no offloading available, accept anything and let the software take care of it. The user wants a LAG and that is the best we can do. - If offloading is available, reject anything that can not be offloaded. My guess is that _any_ hardware offloaded setup will almost always yield a better solution for the user than a software fallback.
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