linux-kernel - Re: [PATCH RESEND bpf-next 01/15] ice: make RX hash reading code more reusable

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Message-ID: <0c40b366-cdb5-f868-00c3-d8f485452cce@intel.com>
Date:   Fri, 19 May 2023 18:46:31 +0200
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Larysa Zaremba <larysa.zaremba@...el.com>
CC:     <bpf@...r.kernel.org>, Stanislav Fomichev <sdf@...gle.com>,
        "Alexei Starovoitov" <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        "KP Singh" <kpsingh@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        Anatoly Burakov <anatoly.burakov@...el.com>,
        Jesper Dangaard Brouer <brouer@...hat.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>,
        <intel-wired-lan@...ts.osuosl.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND bpf-next 01/15] ice: make RX hash reading code more
 reusable

From: Larysa Zaremba <larysa.zaremba@...el.com>
Date: Fri, 12 May 2023 17:25:53 +0200

> Previously, we only needed RX hash 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.
> 
> Separate generic process of reading RX hash from a descriptor
> into a separate function.
> 
> Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>
> ---
>  drivers/net/ethernet/intel/ice/ice_txrx_lib.c | 38 +++++++++++++------
>  1 file changed, 27 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_txrx_lib.c b/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> index c8322fb6f2b3..fc67bbf600af 100644
> --- a/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> +++ b/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> @@ -63,28 +63,44 @@ static enum pkt_hash_types ice_ptype_to_htype(u16 ptype)
>  }
>  
>  /**
> - * ice_rx_hash - set the hash value in the skb
> + * ice_copy_rx_hash_from_desc - copy hash value from descriptor to address
> + * @rx_desc: specific descriptor
> + * @dst: address to copy hash value to
> + *
> + * Returns true, if valid hash has been copied into the destination address.
> + */
> +static bool
> +ice_copy_rx_hash_from_desc(union ice_32b_rx_flex_desc *rx_desc, u32 *dst)

@rx_desc can be const.

I'm also unsure about the naming. Why not name this one ice_rx_hash()
and the one which sets it in skb ice_rx_hash_skb()?

> +{
> +	struct ice_32b_rx_flex_desc_nic *nic_mdid;

Also const. I thought you'll pick most of my optimizations from the
related commit :D

> +
> +	if (rx_desc->wb.rxdid != ICE_RXDID_FLEX_NIC)
> +		return false;
> +
> +	nic_mdid = (struct ice_32b_rx_flex_desc_nic *)rx_desc;
> +	*dst = le32_to_cpu(nic_mdid->rss_hash);
> +	return true;

You can just return the hash. `hash == 0` means there's no hash, so it
basically means `false`, while non-zero is `true`.

> +}
> +
> +/**
> + * ice_rx_hash_to_skb - set the hash value in the skb
>   * @rx_ring: descriptor ring
>   * @rx_desc: specific descriptor
>   * @skb: pointer to current skb
>   * @rx_ptype: the ptype value from the descriptor
>   */
>  static void
> -ice_rx_hash(struct ice_rx_ring *rx_ring, union ice_32b_rx_flex_desc *rx_desc,
> -	    struct sk_buff *skb, u16 rx_ptype)
> +ice_rx_hash_to_skb(struct ice_rx_ring *rx_ring,
> +		   union ice_32b_rx_flex_desc *rx_desc,
> +		   struct sk_buff *skb, u16 rx_ptype)
>  {
> -	struct ice_32b_rx_flex_desc_nic *nic_mdid;
>  	u32 hash;
>  
>  	if (!(rx_ring->netdev->features & NETIF_F_RXHASH))
>  		return;
>  
> -	if (rx_desc->wb.rxdid != ICE_RXDID_FLEX_NIC)
> -		return;
> -
> -	nic_mdid = (struct ice_32b_rx_flex_desc_nic *)rx_desc;
> -	hash = le32_to_cpu(nic_mdid->rss_hash);
> -	skb_set_hash(skb, hash, ice_ptype_to_htype(rx_ptype));
> +	if (ice_copy_rx_hash_from_desc(rx_desc, &hash))

likely()? I wouldn't care about zero-hashed frames, their perf is not
critical anyway.

> +		skb_set_hash(skb, hash, ice_ptype_to_htype(rx_ptype));
>  }
>  
>  /**
> @@ -186,7 +202,7 @@ ice_process_skb_fields(struct ice_rx_ring *rx_ring,
>  		       union ice_32b_rx_flex_desc *rx_desc,
>  		       struct sk_buff *skb, u16 ptype)
>  {
> -	ice_rx_hash(rx_ring, rx_desc, skb, ptype);
> +	ice_rx_hash_to_skb(rx_ring, rx_desc, skb, ptype);
>  
>  	/* modifies the skb - consumes the enet header */
>  	skb->protocol = eth_type_trans(skb, rx_ring->netdev);

Thanks,
Olek