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

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Date: Thu, 20 Jul 2023 15:41:53 +0000
From: "Zaremba, Larysa" <larysa.zaremba@...el.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
CC: Willem de Bruijn <willemdebruijn.kernel@...il.com>, "bpf@...r.kernel.org"
	<bpf@...r.kernel.org>, "ast@...nel.org" <ast@...nel.org>,
	"daniel@...earbox.net" <daniel@...earbox.net>, "andrii@...nel.org"
	<andrii@...nel.org>, "martin.lau@...ux.dev" <martin.lau@...ux.dev>,
	"song@...nel.org" <song@...nel.org>, "yhs@...com" <yhs@...com>,
	"john.fastabend@...il.com" <john.fastabend@...il.com>, "kpsingh@...nel.org"
	<kpsingh@...nel.org>, "sdf@...gle.com" <sdf@...gle.com>, "haoluo@...gle.com"
	<haoluo@...gle.com>, "jolsa@...nel.org" <jolsa@...nel.org>, David Ahern
	<dsahern@...il.com>, Jakub Kicinski <kuba@...nel.org>, Willem de Bruijn
	<willemb@...gle.com>, "Brouer, Jesper" <brouer@...hat.com>, "Burakov,
 Anatoly" <anatoly.burakov@...el.com>, "Lobakin, Aleksander"
	<aleksander.lobakin@...el.com>, Magnus Karlsson <magnus.karlsson@...il.com>,
	"Tahhan, Maryam" <mtahhan@...hat.com>, "xdp-hints@...-project.net"
	<xdp-hints@...-project.net>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 13/21] ice: Implement checksum hint

On Thu, Jul 20, 2023 at 08:14:52AM -0700, Alexei Starovoitov wrote:
> On Thu, Jul 20, 2023 at 2:47 AM Zaremba, Larysa
> <larysa.zaremba@...el.com> wrote:
> >
> > 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@...el.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;

I'll duplicate an improved version of this line from another thread in case it 
could help with the comprehension during review:

*csum_status = XDP_CHECKSUM_VALID_LVL0 + ice_rx_csum_lvl(status);

> > > > > + 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.
> 
> csum kfunc supposed to be generic.
> If for ICE it fills in one argument and for veth another then the whole
> idea of generic api is not working.

Both ice and veth fill in the csum_status, the need to fill in the csum_info is 
determined by the status. I don not see a problem with that.

Maybe you have an issue with putting a valid checksum number into a status 
instead of info? Please clarify.