Re: [dpdk-dev] [PATCH 2/5] net/tap: do not touch Tx offload flags

From: David Marchand <david.marchand@redhat.com>
To: Olivier Matz <olivier.matz@6wind.com>
Cc: Flavio Leitner <fbl@sysclose.org>, dev <dev@dpdk.org>,
	 Maxime Coquelin <maxime.coquelin@redhat.com>,
	Ilya Maximets <i.maximets@ovn.org>,
	 Keith Wiles <keith.wiles@intel.com>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>,
	 Thomas Monjalon <thomas@monjalon.net>,
	Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Subject: Re: [dpdk-dev] [PATCH 2/5] net/tap: do not touch Tx offload flags
Date: Wed, 28 Apr 2021 14:17:35 +0200	[thread overview]
Message-ID: <CAJFAV8xsXyPnMK6nXoDg_e4euDrd-jdd3kS5zQohS+3bfokpxw@mail.gmail.com> (raw)
In-Reply-To: <20210409133018.GB1650@platinum>

On Fri, Apr 9, 2021 at 3:30 PM Olivier Matz <olivier.matz@6wind.com> wrote:
> > I see your point. Going back to improving the documentation as a
> > first step, what would be the next steps? Are we going to wait few
> > releases and then remove the flag tweaking code assuming that PMDs
> > and apps are ok?
>
> After this documentation step, in few releases, we could relax the
> constraint on PMD: applications will be expected to set TCP_CKSUM when
> TCP_SEG is set, so no need for the PMD to force TCP_CKSUM to 1 if
> TCP_SEG is set. The documentation will be updated again.
>
> This plan can be described in the deprecation notice, and later in the
> release note.

Looking at drivers, some of them already trigger tcp checksumming with
the presence of PKT_TX_TCP_SEG only.
See for example:
https://git.dpdk.org/dpdk/tree/drivers/net/ixgbe/ixgbe_rxtx.c#n391

The hw needs to fill tcp checksum when generating segments.
So I suppose this was the original meaning of the "implies" comment.
https://git.dpdk.org/dpdk/tree/lib/mbuf/rte_mbuf_core.h#n292

We could reword the comment, but I don't think there is anything to
change in the API.

-- 
David Marchand