Hi Jiayu, Please find comments inline > -----Original Message----- > From: Hu, Jiayu [mailto:jiayu...@intel.com] > Sent: Monday, April 23, 2018 7:14 AM > To: Ophir Munk <ophi...@mellanox.com>; dev@dpdk.org; Ananyev, > Konstantin <konstantin.anan...@intel.com> > Cc: Thomas Monjalon <tho...@monjalon.net>; Olga Shern > <ol...@mellanox.com>; Pascal Mazon <pascal.ma...@6wind.com>; > sta...@dpdk.org > Subject: RE: [PATCH v1] gso: fix marking TCP checksum flag in TCP segments > > Hi Ophir, > > In the GSO design, the GSO library doesn't care about checksums, which > means it doesn't check if input packets have correct checksums, and it > doesn't do any checksum related work for the output GSO segments. It > depends on the callers to use HW or SW checksum calculation for output > packets. This is why the GSO library doesn't set PKT_TX_TCP_CKSUM. So I > don't think it's a bug. >
Can you please reconsider this design? I think the GSO library should imitate the HW behavior where TCP segments checksum is automatically calculated without explicitly requesting it. I am not saying that GSO library itself should calculate the checksums - but at least it should mark each segment as requiring this calculation. > In my opinion, it's not a good idea to enable HW TCP checksum calculation > silently, and without the aware of the caller. In fact, the caller always > know it > does SW TSO (i.e. GSO), instead of real HW TSO. This is not correct. Consider net_failsafe with 2 sub-devices: one is a HW PCI device, the other one is a SW TAP device. Failsafe must work transparently with these two sub-devices and the caller cannot tell if TSO is done in SW or HW. > If the caller wants HW > checksum calculation, it can add PKT_TX_TCP_CKSUM to ol_flags before or > after calling the GSO library. > FYI - TAP TSO patches were submitted to dpdk.org mailing list. These patches use the GSO library. https://dpdk.org/dev/patchwork/patch/38666/ https://dpdk.org/dev/patchwork/patch/38667/ Running testpmd with TAP TSO is currently broken without the suggested librte_gso patch. Please note testpmd implementation (app/test-pmd/csumonly.c b/app/test-pmd/csumonly.c) in case *both* TSO and TCP CKSUM are configured: if (tso_segsz) ol_flags |= PKT_TX_TCP_SEG; // *** if TSO is applicable - the packet flags are only marked with PKT_TX_TCP_SEG and no PKT_TX_TCP_CKSUM *** else if (tx_offloads & DEV_TX_OFFLOAD_TCP_CKSUM) ol_flags |= PKT_TX_TCP_CKSUM; // *** PKT_TX_TCP_CKSUM is marked only if TSO is not applicable *** else { tcp_hdr->cksum = get_udptcp_checksum(l3_hdr, tcp_hdr, In other words - testpmd does not set TCP_CKSUM along with TCP_SEG therefore using testpmd with TAP/TSO will result in TCP segments with 0 (incorrect) TCP checksums. In addition - please note the comments in lib/librte_mbuf/rte_mbuf.h which specify that PKT_TX_TCP_SEG flag implies the PKT_TX_TCP_CKSUM (hence it is not required to be explicitly set by the caller) /** * TCP segmentation offload. To enable this offload feature for a * packet to be transmitted on hardware supporting TSO: * - set the PKT_TX_TCP_SEG flag in mbuf->ol_flags (this flag implies * PKT_TX_TCP_CKSUM) ... > Add Konstantin for more suggestions. > > Thanks, > Jiayu > > > -----Original Message----- > > From: Ophir Munk [mailto:ophi...@mellanox.com] > > Sent: Sunday, April 22, 2018 10:21 PM > > To: dev@dpdk.org; Hu, Jiayu <jiayu...@intel.com> > > Cc: Thomas Monjalon <tho...@monjalon.net>; Olga Shern > > <ol...@mellanox.com>; Pascal Mazon <pascal.ma...@6wind.com>; > Ophir > > Munk <ophi...@mellanox.com>; sta...@dpdk.org > > Subject: [PATCH v1] gso: fix marking TCP checksum flag in TCP segments > > > > Large TCP packets which are marked with PKT_TX_TCP_SEG flag are > > segmented and the flag is cleared in the resulting segments, however, > > the segments checksum is not updated. It is therefore required to set > > the PKT_TX_TCP_CKSUM flag in each TCP segment in order to mark for the > > sending driver the need to update the TCP checksum before transmitting > > the segment. > > > > Fixes: 119583797b6a ("gso: support TCP/IPv4 GSO") > > Cc: sta...@dpdk.org > > > > Signed-off-by: Ophir Munk <ophi...@mellanox.com> > > --- > > lib/librte_gso/rte_gso.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/lib/librte_gso/rte_gso.c b/lib/librte_gso/rte_gso.c index > > a44e3d4..e9ce9ce 100644 > > --- a/lib/librte_gso/rte_gso.c > > +++ b/lib/librte_gso/rte_gso.c > > @@ -50,12 +50,14 @@ rte_gso_segment(struct rte_mbuf *pkt, > > ((IS_IPV4_GRE_TCP4(pkt->ol_flags) && > > (gso_ctx->gso_types & > > DEV_TX_OFFLOAD_GRE_TNL_TSO)))) { > > pkt->ol_flags &= (~PKT_TX_TCP_SEG); > > + pkt->ol_flags |= PKT_TX_TCP_CKSUM; > > ret = gso_tunnel_tcp4_segment(pkt, gso_size, ipid_delta, > > direct_pool, indirect_pool, > > pkts_out, nb_pkts_out); > > } else if (IS_IPV4_TCP(pkt->ol_flags) && > > (gso_ctx->gso_types & > > DEV_TX_OFFLOAD_TCP_TSO)) { > > pkt->ol_flags &= (~PKT_TX_TCP_SEG); > > + pkt->ol_flags |= PKT_TX_TCP_CKSUM; > > ret = gso_tcp4_segment(pkt, gso_size, ipid_delta, > > direct_pool, indirect_pool, > > pkts_out, nb_pkts_out); > > -- > > 2.7.4
