netdev - Re: [PATCH net-next 1/8] qed: LL2 to use packed information for tx

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Message-Id: <20170608.192358.1444190196602150329.davem@davemloft.net>
Date:   Thu, 08 Jun 2017 19:23:58 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     Yuval.Mintz@...ium.com
Cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        Michal.Kalderon@...ium.com
Subject: Re: [PATCH net-next 1/8] qed: LL2 to use packed information for tx

From: Yuval Mintz <Yuval.Mintz@...ium.com>
Date: Thu, 8 Jun 2017 19:13:16 +0300

> @@ -67,6 +79,21 @@ struct qed_ll2_stats {
>  	u64 sent_bcast_pkts;
>  };
>  
> +struct qed_ll2_tx_pkt_info {
> +	u8 num_of_bds;
> +	u16 vlan;
> +	u8 bd_flags;
> +	u16 l4_hdr_offset_w;	/* from start of packet */
> +	enum qed_ll2_tx_dest tx_dest;
> +	enum qed_ll2_roce_flavor_type qed_roce_flavor;
> +	dma_addr_t first_frag;
> +	u16 first_frag_len;
> +	bool enable_ip_cksum;
> +	bool enable_l4_cksum;
> +	bool calc_ip_len;
> +	void *cookie;
> +};
> +

This layout is extremely inefficient, with lots of padding in between
struct members.

Group small u8 members and u16 members together so that they consume
full 32-bit areas so you can eliminate all of the padding.