Hi Thomas, Thank for your comments. My responses are inline.
> -----Original Message----- > From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com] > Sent: Monday, October 20, 2014 1:30 PM > To: Walukiewicz, Miroslaw > Cc: dev at dpdk.org > Subject: Re: [dpdk-dev] [PATCH] pmd: Add generic support for TCP TSO > (Transmit Segmentation Offload) > > Hi Miroslaw, > > I'll try to comment your patch, but I don't know if you'll receive it. > Indeed, you didn't reply to the previous comments. > Please configure your email client to receive these emails. > This is not a write-only list. > > 2014-10-20 05:42, miroslaw.walukiewicz at intel.com: > > Add new PKT_TX_TCP_SEG flag > > Add new fields in the tx offload fields indicating MSS and L4 len > > You should explain why these additions are needed. I will resend a patch with better description of new fields. > > > /* fields to support TX offloads */ > > - union { > > - uint16_t l2_l3_len; /**< combined l2/l3 lengths as single var > */ > > - struct { > > - uint16_t l3_len:9; /**< L3 (IP) Header Length. */ > > - uint16_t l2_len:7; /**< L2 (MAC) Header Length. > */ > > + /* two bytes - l2/l3 len for compatibility (endian issues) > > + * two bytes - reseved for alignment > > + * two bytes - l4 len (TCP/UDP) header len > > + * two bytes - TCP tso segment size > > + */ > > + struct { > > + union { > > + uint16_t l2_l3_len; /**< combined l2/l3 len */ > > + struct { > > + uint16_t l3_len:9; /**< L3 (IP) Header */ > > + uint16_t l2_len:7; /**< L2 (MAC) Header */ > > + }; > > }; > > Why nesting these fields in an anonymous structure? I want to keep a source compatibility with non-TSO applications using that field for example IP checksum computing by NIC. Keeping this structure anonymous I do not require changes in old applications that do not need TSO support. The second argument is that in original patch extending the rte_mbuf to 128 bytes made by Bruce the author made this structure anonymous and I follow this assumption too. > > > + uint16_t reserved_tx_offload; > > + uint16_t l4_len; /**< TCP/UDP header len */ > > + uint16_t tso_segsz; /**< TCP TSO segment size */ > > }; > > What means reserved_tx_offload? It is really for alignment. I want to keep all this structure 8 byte long. Really I found an issue in my patch. I think that all tx offload fields should be available in single 64-bit dword to make correct operation on in pkt_mbuf_reset and pkt_mbuf_attach. Today these macros use only first 32-bits from structure and keeps l4_len and tso_segsz untouched. I will modify my patch also in this direction. > > Is there an impact on performance of actual drivers ? > I did not observed on my machine any significant differences when aligned and non-aligned structure is used. I agree that alignment is important for small packets. The TSO is used for using very long TCP segments usually. > How this patch is related with previous work in progress about TSO? > As the original Bruce's patch defining a new rte_mbuf structure did not follow exactly the concept proposed by Olivier Matz I made the closest approximation. I defined PKT_TX_TCP_SEG, l4_len, mss = tso_segsz Using mss could be misinterpreted. I think tso_segsz much better describes this field meaning. I completely agree that the pseudo header checksum could be computed outside driver and I also followed this assumption. Mirek > -- > Thomas
