netdev - Re: [Question] About bonding offload

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Date:   Tue, 11 Apr 2023 13:15:49 +0800
From:   Liang Li <liali@...hat.com>
To:     Jay Vosburgh <jay.vosburgh@...onical.com>
Cc:     vfalico@...il.com, andy@...yhouse.net, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org,
        Paolo Abeni <pabeni@...hat.com>, ast@...nel.org,
        daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hangbin Liu <haliu@...hat.com>,
        "Toppins, Jonathan" <jtoppins@...hat.com>
Subject: Re: [Question] About bonding offload

Thanks everyone! Glad to know this.

On Tue, Apr 11, 2023 at 12:58 PM Jay Vosburgh
<jay.vosburgh@...onical.com> wrote:
>
> Liang Li <liali@...hat.com> wrote:
>
> >Hi Everyone,
> >
> >I'm a redhat network-qe and am testing bonding offload. e.g. gso,tso,gro,lro.
> >I got two questions during my testing.
> >
> >1. The tcp performance has no difference when bonding GRO is on versus off.
> >When testing with bonding, I always get ~890 Mbits/sec bandwidth no
> >matter whether GRO is on.
> >When testing with a physical NIC instead of bonding on the same
> >machine, with GRO off, I get 464 Mbits/sec bandwidth, with GRO on, I
> >get  897 Mbits/sec bandwidth.
> >So looks like the GRO can't be turned off on bonding?
>
>         Well, it's probably more correct to say that GRO is
> unimplemented for "stacked on top" interfaces like bonding (or bridge,
> vlan, team, etc).  GRO operates early in the receive processing, when
> the device driver is receiving packets, typically by calling
> napi_gro_receive() from its NAPI poll function.  This is well before
> bonding, bridge, et al, are involved, as these drivers don't do NAPI at
> all.
>
> >I used iperf3 to test performance.
> >And I limited iperf3 process cpu usage during my testing to simulate a
> >cpu bottleneck.
> >Otherwise it's difficult to see bandwidth differences when offload is
> >on versus off.
> >
> >I reported a bz for this: https://bugzilla.redhat.com/show_bug.cgi?id=2183434
> >
> >2.  Should bonding propagate offload configuration to slaves?
> >For now, only "ethtool -K bond0 lro off" can be propagated to slaves,
> >others can't be propagated to slaves, e.g.
> >  ethtool -K bond0 tso on/off
> >  ethtool -K bond0 gso on/off
> >  ethtool -K bond0 gro on/off
> >  ethtool -K bond0 lro on
> >All above configurations can't be propagated to bonding slaves.
>
>         The LRO case is because it's set in NETIF_F_UPPER_DISABLES, as
> checked in netdev_sync_upper_features() and netdev_sync_lower_features().
>
>         A subset of features is handled in bond_compute_features().
> Some feature changes, e.g., scatter-gather, do propagate upwards (but
> not downwards), as bonding handles NETDEV_FEAT_CHANGE events for its
> members (but not vice versa).
>
>         TSO, GSO, and GRO aren't handled in either of these situations,
> and so changes don't propagate at all.  Whether they should or not is a
> separate, complicated, question.  E.g., should features propagate
> upwards, or downwards?  How many levels of nesting?
>
>         -J
>
> >I reports a bz for this: https://bugzilla.redhat.com/show_bug.cgi?id=2183777
> >
> >I am using the RHEL with kernel 4.18.0-481.el8.x86_64.
> >
> >BR,
> >Liang Li
> >
>
> ---
>         -Jay Vosburgh, jay.vosburgh@...onical.com
>