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 11:45:36 +0000 Message-ID: References: <1524406859-29585-1-git-send-email-ophirmu@mellanox.com> <2601191342CEEE43887BDE71AB977258AEA5081C@IRSMSX102.ger.corp.intel.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: "Ananyev, Konstantin" , "Hu, Jiayu" , "dev@dpdk.org" Return-path: In-Reply-To: <2601191342CEEE43887BDE71AB977258AEA5081C@IRSMSX102.ger.corp.intel.com> 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 Konstantin, Please see inline > -----Original Message----- > From: Ananyev, Konstantin [mailto:konstantin.ananyev@intel.com] > Sent: Tuesday, April 24, 2018 1:56 PM > To: Ophir Munk ; Hu, Jiayu ; > dev@dpdk.org > 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 >=20 >=20 > > -----Original Message----- > > From: Ophir Munk [mailto:ophirmu@mellanox.com] > > Sent: Tuesday, April 24, 2018 10:44 AM > > To: Hu, Jiayu ; 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 > > segments > > > > 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 > > > 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 l= ibrary > itself should calculate the checksums - but at least it should mark each > segment as requiring this calculation. >=20 > But gso has no idea how this packet will be processed after it. GSO shouldn't know. It should only mark the fact that a new TCP segment was= created without a TCP checksum.=20 > Caller can choose to calculate L3/L4 cksum in SW or might be going to use > HW offloads. Assuming TSO is configured then you suggest that TAP PMD will mark by itsel= f the TCP_CKSUM flag for all packets returned from GSO library? > In later case nothing stops the caller to update mbuf->ol_flags in a way = he > likes (TCP_CKSUM, IP_CKSUM, etc.). > Konstantin >=20 Please note that TCP_SEG flag is cleared by GSO library in 2 different case= s: 1. Packet length equals to or is bigger than GSO size. In this case new TCP= segments are created with no TCP checksum.=20 2. Packet length is smaller than GSO size. In this case no TCP segmentation= is required. The original packet is returned and its existing TCP checksum= is OK. In the latter case TAP PMD will always calculate TCP checksum in SW (perfor= mance concerns) where this could have been saved.=20 I am thinking of a practical scenario where TSO is configured but all packe= ts are smaller than GSO size, however TAP PMD unnecessarily recalculates th= eir checksums. How do you suggest to avoid this scenario? > > > > > 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 TS= O 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://emea01.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Fdpd > > > k.org%2Fdev%2Fpatchwork%2Fpatch%2F38666%2F&data=3D02%7C01%7Coph > irmu%40me > > > llanox.com%7C7455c8e31c7a4364bc7108d5a9d20008%7Ca652971c7d2e4d > 9ba6a4d1 > > > 49256f461b%7C0%7C0%7C636601641779974217&sdata=3DCF7EvhXG%2BrH% > 2BPiQEbvM0 > > mC%2FSpqobneKaoV03j5VrSDw%3D&reserved=3D0 > > > https://emea01.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Fdpd > > > k.org%2Fdev%2Fpatchwork%2Fpatch%2F38667%2F&data=3D02%7C01%7Coph > irmu%40me > > > llanox.com%7C7455c8e31c7a4364bc7108d5a9d20008%7Ca652971c7d2e4d > 9ba6a4d1 > > > 49256f461b%7C0%7C0%7C636601641779974217&sdata=3Dj9WVIj%2FKq6EN > WXu3mr5By1 > > toSowU8bqJRGZ19SxiGoI%3D&reserved=3D0 > > > > 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 |=3D PKT_TX_TCP_SEG; // *** if TSO is applicable - th= e 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 |=3D PKT_TX_TCP_CKSUM; // *** PKT_TX_TCP_CKSUM is > marked 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 > > 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: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