netdev - Re: [PATCH net-next v5 2/7] net: ethtool: add tcp_data_split_mod member in kernel_ethtool

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Message-ID: <CAMArcTWfxiKWghy3cFEL4rj7=VKku_Sm4W9pVWk39TEae1fyAw@mail.gmail.com>
Date: Sat, 16 Nov 2024 02:17:55 +0900
From: Taehee Yoo <ap420073@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
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Subject: Re: [PATCH net-next v5 2/7] net: ethtool: add tcp_data_split_mod
 member in kernel_ethtool_ringparam

On Fri, Nov 15, 2024 at 1:22 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Wed, 13 Nov 2024 17:32:16 +0000 Taehee Yoo wrote:
> > When tcp-data-split is UNKNOWN mode, drivers arbitrarily handle it.
> > For example, bnxt_en driver automatically enables if at least one of
> > LRO/GRO/JUMBO is enabled.
> > If tcp-data-split is UNKNOWN and LRO is enabled, a driver returns
> > ENABLES of tcp-data-split, not UNKNOWN.
> > So, `ethtool -g eth0` shows tcp-data-split is enabled.
> >
> > The problem is in the setting situation.
> > In the ethnl_set_rings(), it first calls get_ringparam() to get the
> > current driver's config.
> > At that moment, if driver's tcp-data-split config is UNKNOWN, it returns
> > ENABLE if LRO/GRO/JUMBO is enabled.
> > Then, it sets values from the user and driver's current config to
> > kernel_ethtool_ringparam.
> > Last it calls .set_ringparam().
> > The driver, especially bnxt_en driver receives
> > ETHTOOL_TCP_DATA_SPLIT_ENABLED.
> > But it can't distinguish whether it is set by the user or just the
> > current config.
> >
> > The new tcp_data_split_mod member indicates the tcp-data-split value is
> > explicitly set by the user.
> > So the driver can handle ETHTOOL_TCP_DATA_SPLIT_ENABLED properly.
>
> I think this can work, but it isn't exactly what I had in mind.
>
> I was thinking we'd simply add u8 hds_config to
> struct ethtool_netdev_state (which is stored inside netdev).
> And update it there if user request via ethnl_set_rings() succeeds.
>
> That gives the driver and the core quick and easy access to checking if
> the user forced the setting to ENABLED or DISABLED, or didn't (UNKNOWN).
>
> As far as the parameter passed to ->set_ringparam() goes we could do
> (assuming the new fields in ethtool_netdev state is called hds):
>
>         kernel_ringparam.tcp_data_split =
>                 nla_get_u32_default(tb[ETHTOOL_A_RINGS_TCP_DATA_SPLIT],
>                                     dev->ethtool->hds);
>
> If the driver see UNKNOWN it means user doesn't care.
> If the driver sees ENABLED/DISABLE it must comply, doesn't matter if
> the user requested it in current netlink call, or previous and hasn't
> reset it, yet.
>
> Hope this makes sense...

Thank you so much for the details!
I will try to use ethtool_netdev_state instead of this approach.

Thanks a lot!
Taehee Yoo