netdev - Re: [PATCH net-next] bonding: add software timestamping support

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Date:   Wed, 29 Mar 2023 21:07:59 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Hangbin Liu <liuhangbin@...il.com>
Cc:     Miroslav Lichvar <mlichvar@...hat.com>, netdev@...r.kernel.org,
        Jay Vosburgh <j.vosburgh@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jonathan Toppins <jtoppins@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Richard Cochran <richardcochran@...il.com>
Subject: Re: [PATCH net-next] bonding: add software timestamping support

On Thu, 30 Mar 2023 11:33:43 +0800 Hangbin Liu wrote:
> On Wed, Mar 29, 2023 at 12:27:11PM +0200, Miroslav Lichvar wrote:
> > On Wed, Mar 29, 2023 at 11:13:37AM +0800, Hangbin Liu wrote:  
> > > At present, bonding attempts to obtain the timestamp (ts) information of
> > > the active slave. However, this feature is only available for mode 1, 5,
> > > and 6. For other modes, bonding doesn't even provide support for software
> > > timestamping. To address this issue, let's call ethtool_op_get_ts_info
> > > when there is no primary active slave. This will enable the use of software
> > > timestamping for the bonding interface.  
> > 
> > Would it make sense to check if all devices in the bond support
> > SOF_TIMESTAMPING_TX_SOFTWARE before returning it for the bond?
> > Applications might expect that a SW TX timestamp will be always
> > provided if the capability is reported.  
> 
> In my understanding this is a software feature, no need for hardware support.
> In __sock_tx_timestamp() it will set skb tx_flags when we have
> SOF_TIMESTAMPING_TX_SOFTWARE flag. Do I understand wrong?

Driver needs to call skb_tx_timestamp(), so unlike with Rx there's
something to do for the driver.