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Date: Fri, 9 Jun 2017 08:23:30 +0000 From: David Laight <David.Laight@...LAB.COM> To: "'Mintz, Yuval'" <Yuval.Mintz@...ium.com>, 'David Miller' <davem@...emloft.net> CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>, "Kalderon, Michal" <Michal.Kalderon@...ium.com> Subject: RE: [PATCH net-next 1/8] qed: LL2 to use packed information for tx From: Mintz, Yuval > Sent: 09 June 2017 08:52 > > From: David Laight [mailto:David.Laight@...LAB.COM] > > Sent: Friday, June 09, 2017 10:28 AM > > To: 'David Miller' <davem@...emloft.net>; Mintz, Yuval > > <Yuval.Mintz@...ium.com> > > Cc: netdev@...r.kernel.org; linux-rdma@...r.kernel.org; Kalderon, Michal > > <Michal.Kalderon@...ium.com> > > Subject: RE: [PATCH net-next 1/8] qed: LL2 to use packed information for tx > > > > From: David Miller > > > Sent: 09 June 2017 00:24 > > > > > > 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. > > > > I'd also query the use of u16 sizes/lengths, any arithmetic on u16 (and u8) > > variables is likely to generate extra code (on non-x86). > > You are using 32 bits for the 'enum' - I bet the values fit in 8 bits, so aren't > > really worried about size. > > > > If size did matter you can easily get the above down to 32 bytes. > > You're right, and that's exactly the point - since this is not data-path critical > I don't see why the size/efficiency should matter [greatly]. It is just good practise so that it happens automatically when it does matter. Just swapping 'vlan' and 'bd_flags' would make it look much better. David
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