Re: [PATCH bpf-next v3 13/21] ice: Implement checksum hint

From: "Zaremba, Larysa" <larysa.zaremba@intel.com>
To: Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	"ast@kernel.org" <ast@kernel.org>,
	"daniel@iogearbox.net" <daniel@iogearbox.net>,
	"andrii@kernel.org" <andrii@kernel.org>,
	"martin.lau@linux.dev" <martin.lau@linux.dev>,
	"song@kernel.org" <song@kernel.org>, "yhs@fb.com" <yhs@fb.com>,
	"john.fastabend@gmail.com" <john.fastabend@gmail.com>,
	"kpsingh@kernel.org" <kpsingh@kernel.org>,
	"sdf@google.com" <sdf@google.com>,
	"haoluo@google.com" <haoluo@google.com>,
	"jolsa@kernel.org" <jolsa@kernel.org>,
	David Ahern <dsahern@gmail.com>, Jakub Kicinski <kuba@kernel.org>,
	Willem de Bruijn <willemb@google.com>,
	"Brouer, Jesper" <brouer@redhat.com>,
	"Burakov, Anatoly" <anatoly.burakov@intel.com>,
	"Lobakin, Aleksander" <aleksander.lobakin@intel.com>,
	Magnus Karlsson <magnus.karlsson@gmail.com>,
	"Tahhan, Maryam" <mtahhan@redhat.com>,
	"xdp-hints@xdp-project.net" <xdp-hints@xdp-project.net>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next v3 13/21] ice: Implement checksum hint
Date: Thu, 20 Jul 2023 09:47:16 +0000	[thread overview]
Message-ID: <ZLkBrfex1ENbVDwF@lincoln> (raw)
In-Reply-To: <64b85ad52d012_2849c1294df@willemb.c.googlers.com.notmuch>

On Wed, Jul 19, 2023 at 05:51:17PM -0400, Willem de Bruijn wrote:
> Alexei Starovoitov wrote:
> > On Wed, Jul 19, 2023 at 08:37:26PM +0200, Larysa Zaremba wrote:
> > > Implement .xmo_rx_csum callback to allow XDP code to determine,
> > > whether HW has validated any checksums.
> > > 
> > > Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> > > ---
> > >  drivers/net/ethernet/intel/ice/ice_txrx_lib.c | 29 +++++++++++++++++++
> > >  1 file changed, 29 insertions(+)
> > > 
> > > diff --git a/drivers/net/ethernet/intel/ice/ice_txrx_lib.c b/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> > > index 54685d0747aa..6647a7e55ac8 100644
> > > --- a/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> > > +++ b/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> > > @@ -660,8 +660,37 @@ static int ice_xdp_rx_vlan_tag(const struct xdp_md *ctx, u16 *vlan_tci,
> > >  	return 0;
> > >  }
> > >  
> > > +/**
> > > + * ice_xdp_rx_csum_lvl - Get level, at which HW has checked the checksum
> > > + * @ctx: XDP buff pointer
> > > + * @csum_status: destination address
> > > + * @csum_info: destination address
> > > + *
> > > + * Copy HW checksum level (if was checked) to the destination address.
> > > + */
> > > +static int ice_xdp_rx_csum(const struct xdp_md *ctx,
> > > +			   enum xdp_csum_status *csum_status,
> > > +			   union xdp_csum_info *csum_info)
> > > +{
> > > +	const struct ice_xdp_buff *xdp_ext = (void *)ctx;
> > > +	const union ice_32b_rx_flex_desc *eop_desc;
> > > +	enum ice_rx_csum_status status;
> > > +	u16 ptype;
> > > +
> > > +	eop_desc = xdp_ext->pkt_ctx.eop_desc;
> > > +	ptype = ice_get_ptype(eop_desc);
> > > +
> > > +	status = ice_get_rx_csum_status(eop_desc, ptype);
> > > +	if (status & ICE_RX_CSUM_NONE)
> > > +		return -ENODATA;
> > > +
> > > +	*csum_status = ice_rx_csum_lvl(status) + 1;
> > > +	return 0;
> > > +}
> > 
> > and xdp_csum_info from previous patch left uninitialized?
> > What was the point adding it then?
> 
> I suppose this driver only returns CHECKSUM_NONE or
> CHECKSUM_UNNECESSARY? Also based on a grep of the driver dir.
> 

Yes, correct, current ice HW cannot produce complete checksum,
so only CHECKSUM_UNNECESSARY for known protocols, CHECKSUM_NONE otherwise,
nothing to initialize csum_info with in either case.

xdp_csum_info is initialized in veth implementation though, but only 
csum_start/offset, so complete XDP checksum has no users in this patchset.
Is this a problem?

In previous version I had CHECKSUM_UNNECESSARY-only kfunc, but I think everyone 
has agreed, csum hint kfunc should give more comprehensive output.

> In general the layout makes sense to me, and +1 on supporting
> other drivers that do return CHECKSUM_COMPLETE or CHECKSUM_PARTIAL
> rigth from the start.
> 