netdev - Re: [xdp-hints] [RFC bpf-next 03/23] ice: make RX checksum checking code more reusable

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Message-ID: <ZPddEcHOeRrtRcmj@lincoln>
Date: Tue, 5 Sep 2023 18:53:37 +0200
From: Larysa Zaremba <larysa.zaremba@...el.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
CC: <bpf@...r.kernel.org>, <ast@...nel.org>, <daniel@...earbox.net>,
	<andrii@...nel.org>, <martin.lau@...ux.dev>, <song@...nel.org>, <yhs@...com>,
	<john.fastabend@...il.com>, <kpsingh@...nel.org>, <sdf@...gle.com>,
	<haoluo@...gle.com>, <jolsa@...nel.org>, David Ahern <dsahern@...il.com>,
	Jakub Kicinski <kuba@...nel.org>, Willem de Bruijn <willemb@...gle.com>,
	Jesper Dangaard Brouer <brouer@...hat.com>, Anatoly Burakov
	<anatoly.burakov@...el.com>, Alexander Lobakin <alexandr.lobakin@...el.com>,
	Magnus Karlsson <magnus.karlsson@...il.com>, Maryam Tahhan
	<mtahhan@...hat.com>, <xdp-hints@...-project.net>, <netdev@...r.kernel.org>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>, Alexei Starovoitov
	<alexei.starovoitov@...il.com>, Simon Horman <simon.horman@...igine.com>,
	Tariq Toukan <tariqt@...lanox.com>, Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [xdp-hints] [RFC bpf-next 03/23] ice: make RX checksum checking
 code more reusable

On Tue, Sep 05, 2023 at 05:37:27PM +0200, Maciej Fijalkowski wrote:
> On Mon, Sep 04, 2023 at 08:01:06PM +0200, Larysa Zaremba wrote:
> > On Mon, Sep 04, 2023 at 05:02:40PM +0200, Maciej Fijalkowski wrote:
> > > On Thu, Aug 24, 2023 at 09:26:42PM +0200, Larysa Zaremba wrote:
> > > > Previously, we only needed RX checksum flags in skb path,
> > > > hence all related code was written with skb in mind.
> > > > But with the addition of XDP hints via kfuncs to the ice driver,
> > > > the same logic will be needed in .xmo_() callbacks.
> > > > 
> > > > Put generic process of determining checksum status into
> > > > a separate function.
> > > > 
> > > > Now we cannot operate directly on skb, when deducing
> > > > checksum status, therefore introduce an intermediate enum for checksum
> > > > status. Fortunately, in ice, we have only 4 possibilities: checksum
> > > > validated at level 0, validated at level 1, no checksum, checksum error.
> > > > Use 3 bits for more convenient conversion.
> > > > 
> > > > Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>
> > > > ---
> > > >  drivers/net/ethernet/intel/ice/ice_txrx_lib.c | 105 ++++++++++++------
> > > >  1 file changed, 69 insertions(+), 36 deletions(-)
> > > > 
> > > > diff --git a/drivers/net/ethernet/intel/ice/ice_txrx_lib.c b/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> > > > index b2f241b73934..8b155a502b3b 100644
> > > > --- a/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> > > > +++ b/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> > > > @@ -102,18 +102,41 @@ ice_rx_hash_to_skb(const struct ice_rx_ring *rx_ring,
> > > >  		skb_set_hash(skb, hash, ice_ptype_to_htype(rx_ptype));
> > > >  }
> > > >  
> > > > +enum ice_rx_csum_status {
> > > > +	ICE_RX_CSUM_LVL_0	= 0,
> > > > +	ICE_RX_CSUM_LVL_1	= BIT(0),
> > > > +	ICE_RX_CSUM_NONE	= BIT(1),
> > > > +	ICE_RX_CSUM_ERROR	= BIT(2),
> > > > +	ICE_RX_CSUM_FAIL	= ICE_RX_CSUM_NONE | ICE_RX_CSUM_ERROR,
> > > > +};
> > > > +
> > > >  /**
> > > > - * ice_rx_csum - Indicate in skb if checksum is good
> > > > - * @ring: the ring we care about
> > > > - * @skb: skb currently being received and modified
> > > > + * ice_rx_csum_lvl - Get checksum level from status
> > > > + * @status: driver-specific checksum status
> 
> nit: describe retval?
>

I think that kernel-doc is already too much for a one-liner.
Also, checksum level is fully explained in sk_buff documentation.

> > > > + */
> > > > +static u8 ice_rx_csum_lvl(enum ice_rx_csum_status status)
> > > > +{
> > > > +	return status & ICE_RX_CSUM_LVL_1;
> > > > +}
> > > > +
> > > > +/**
> > > > + * ice_rx_csum_ip_summed - Checksum status from driver-specific to generic
> > > > + * @status: driver-specific checksum status
> 
> ditto

Same as above. Moreover, there are only 2 possible return values that anyone can 
easily look up. Describing them here would only balloon the file length.

> 
> > > > + */
> > > > +static u8 ice_rx_csum_ip_summed(enum ice_rx_csum_status status)
> > > > +{
> > > > +	return status & ICE_RX_CSUM_NONE ? CHECKSUM_NONE : CHECKSUM_UNNECESSARY;
> > > 
> > > 	return !(status & ICE_RX_CSUM_NONE);
> > > 
> > > ?
> > 
> > status & ICE_RX_CSUM_NONE ? CHECKSUM_NONE : CHECKSUM_UNNECESSARY;
> > 
> > is immediately understandable and results in 3 asm operations (I have checked):
> > 
> > result = status >> 1;
> > result ^= 1;
> > result &= 1;
> > 
> > I do not think "!(status & ICE_RX_CSUM_NONE);" could produce less.
> 
> oh, nice. Just the fact that branch being added caught my eye.
> 
> (...)