From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ophir Munk Subject: Re: [PATCH v1] gso: fix marking TCP checksum flag in TCP segments Date: Tue, 24 Apr 2018 09:44:18 +0000 Message-ID: References: <1524406859-29585-1-git-send-email-ophirmu@mellanox.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Cc: Thomas Monjalon , Olga Shern , Pascal Mazon , "stable@dpdk.org" To: "Hu, Jiayu" , "dev@dpdk.org" , "Ananyev, Konstantin" Return-path: In-Reply-To: Content-Language: en-US List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" Hi Jiayu, Please find comments inline > -----Original Message----- > From: Hu, Jiayu [mailto:jiayu.hu@intel.com] > Sent: Monday, April 23, 2018 7:14 AM > To: Ophir Munk ; dev@dpdk.org; Ananyev, > Konstantin > Cc: Thomas Monjalon ; Olga Shern > ; Pascal Mazon ; > stable@dpdk.org > Subject: RE: [PATCH v1] gso: fix marking TCP checksum flag in TCP segment= s >=20 > Hi Ophir, >=20 > 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. >=20 Can you please reconsider this design? I think the GSO library should imita= te the HW behavior where TCP segments checksum is automatically calculated = without explicitly requesting it. I am not saying that GSO library itself s= hould 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.=20 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 transparen= tly with these two sub-devices and the caller cannot tell if TSO is done in= SW or HW.=20 > If the caller wants HW > checksum calculation, it can add PKT_TX_TCP_CKSUM to ol_flags before or > after calling the GSO library. >=20 FYI - TAP TSO patches were submitted to dpdk.org mailing list. These patche= s 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 libr= te_gso patch.=20 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 |=3D PKT_TX_TCP_SEG; // *** if TSO is applicable - the pa= cket flags are only marked with PKT_TX_TCP_SEG and no PKT_TX_TCP_CKSUM *** else if (tx_offloads & DEV_TX_OFFLOAD_TCP_CKSUM)=20 ol_flags |=3D PKT_TX_TCP_CKSUM; // *** PKT_TX_TCP_CKSUM is marke= d only if TSO is not applicable *** else { tcp_hdr->cksum =3D get_udptcp_checksum(l3_hdr, tcp_hdr, In other words - testpmd does not set TCP_CKSUM along with TCP_SEG therefor= e 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. >=20 > Thanks, > Jiayu >=20 > > -----Original Message----- > > From: Ophir Munk [mailto:ophirmu@mellanox.com] > > Sent: Sunday, April 22, 2018 10:21 PM > > To: dev@dpdk.org; Hu, Jiayu > > Cc: Thomas Monjalon ; Olga Shern > > ; Pascal Mazon ; > Ophir > > Munk ; stable@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: stable@dpdk.org > > > > Signed-off-by: Ophir Munk > > --- > > 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 &=3D (~PKT_TX_TCP_SEG); > > + pkt->ol_flags |=3D PKT_TX_TCP_CKSUM; > > ret =3D 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 &=3D (~PKT_TX_TCP_SEG); > > + pkt->ol_flags |=3D PKT_TX_TCP_CKSUM; > > ret =3D gso_tcp4_segment(pkt, gso_size, ipid_delta, > > direct_pool, indirect_pool, > > pkts_out, nb_pkts_out); > > -- > > 2.7.4