[dpdk-dev] [PATCH v3 2/5] gso: add TCP/IPv4 GSO support

[Ananyev, Konstantin]

Hi Jiayu,

> -----Original Message-----
> From: Hu, Jiayu
> Sent: Thursday, September 14, 2017 7:07 AM
> To: Ananyev, Konstantin <konstantin.ananyev at intel.com>
> Cc: dev at dpdk.org; Kavanagh, Mark B <mark.b.kavanagh at intel.com>; Tan, Jianfeng <jianfeng.tan at intel.com>
> Subject: Re: [PATCH v3 2/5] gso: add TCP/IPv4 GSO support
> 
> Hi Konstantin,
> 
> On Thu, Sep 14, 2017 at 06:10:37AM +0800, Ananyev, Konstantin wrote:
> >
> > Hi Jiayu,
> >
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Ananyev, Konstantin
> > > > > Sent: Tuesday, September 12, 2017 12:18 PM
> > > > > To: Hu, Jiayu <jiayu.hu at intel.com>; dev at dpdk.org
> > > > > Cc: Kavanagh, Mark B <mark.b.kavanagh at intel.com>; Tan, Jianfeng <jianfeng.tan at intel.com>
> > > > > Subject: RE: [PATCH v3 2/5] gso: add TCP/IPv4 GSO support
> > > > >
> > > > > > result, when all of its GSOed segments are freed, the packet is freed
> > > > > > automatically.
> > > > > > diff --git a/lib/librte_gso/rte_gso.c b/lib/librte_gso/rte_gso.c
> > > > > > index dda50ee..95f6ea6 100644
> > > > > > --- a/lib/librte_gso/rte_gso.c
> > > > > > +++ b/lib/librte_gso/rte_gso.c
> > > > > > @@ -33,18 +33,53 @@
> > > > > >
> > > > > >  #include <errno.h>
> > > > > >
> > > > > > +#include <rte_log.h>
> > > > > > +
> > > > > >  #include "rte_gso.h"
> > > > > > +#include "gso_common.h"
> > > > > > +#include "gso_tcp4.h"
> > > > > >
> > > > > >  int
> > > > > >  rte_gso_segment(struct rte_mbuf *pkt,
> > > > > > -		struct rte_gso_ctx gso_ctx __rte_unused,
> > > > > > +		struct rte_gso_ctx gso_ctx,
> > > > > >  		struct rte_mbuf **pkts_out,
> > > > > >  		uint16_t nb_pkts_out)
> > > > > >  {
> > > > > > +	struct rte_mempool *direct_pool, *indirect_pool;
> > > > > > +	struct rte_mbuf *pkt_seg;
> > > > > > +	uint16_t gso_size;
> > > > > > +	uint8_t ipid_delta;
> > > > > > +	int ret = 1;
> > > > > > +
> > > > > >  	if (pkt == NULL || pkts_out == NULL || nb_pkts_out < 1)
> > > > > >  		return -EINVAL;
> > > > > >
> > > > > > -	pkts_out[0] = pkt;
> > > > > > +	if (gso_ctx.gso_size >= pkt->pkt_len ||
> > > > > > +			(pkt->packet_type & gso_ctx.gso_types) !=
> > > > > > +			pkt->packet_type) {
> > > > > > +		pkts_out[0] = pkt;
> > > > > > +		return ret;
> > > > > > +	}
> > > > > > +
> > > > > > +	direct_pool = gso_ctx.direct_pool;
> > > > > > +	indirect_pool = gso_ctx.indirect_pool;
> > > > > > +	gso_size = gso_ctx.gso_size;
> > > > > > +	ipid_delta = gso_ctx.ipid_flag == RTE_GSO_IPID_INCREASE;
> > > > > > +
> > > > > > +	if (is_ipv4_tcp(pkt->packet_type)) {
> > > > >
> > > > > Probably we need here:
> > > > > If (is_ipv4_tcp(pkt->packet_type)  && (gso_ctx->gso_types & DEV_TX_OFFLOAD_TCP_TSO) != 0) {...
> > > >
> > > > Sorry, actually it probably should be:
> > > > If (pkt->ol_flags & (PKT_TX_TCP_SEG | PKT_TX_IPV4) == PKT_TX_IPV4 &&
> > > >       (gso_ctx->gso_types & DEV_TX_OFFLOAD_TCP_TSO) != 0) {...
> > >
> > > I don't quite understand why the GSO library should be aware if the TSO
> > > flag is set or not. Applications can query device TSO capability before
> > > they call the GSO library. Do I misundertsand anything?
> > >
> > > Additionally, we don't need to check if the packet is a TCP/IPv4 packet here?
> >
> > Well, right now  PMD we doesn't rely on ptype to figure out what type of packet and
> > what TX offload have to be performed.
> > Instead it looks at TX part of ol_flags, and
> > My thought was that as what we doing is actually TSO in SW, it would be good
> > to use the same API here too.
> > Also with that approach, by setting ol_flags properly user can use the same gso_ctx and still
> > specify what segmentation to perform on a per-packet basis.
> >
> > Alternative way is to rely on ptype to distinguish should segmentation be performed on that package or not.
> > The only advantage I see here is that if someone would like to add GSO for some new protocol,
> > he wouldn't need to introduce new TX flag value for mbuf.ol_flags.
> > Though he still would need to update TX_OFFLOAD_* capabilities and probably packet_type definitions.
> >
> > So from my perspective first variant (use HW TSO API) is more plausible.
> > Wonder what is your and Mark opinions here?
> 
> In the first choice, you mean:
> the GSO library uses gso_ctx->gso_types and mbuf->ol_flags to call a specific GSO
> segmentation function (e.g. gso_tcp4_segment(), gso_tunnel_xxx()) for each input packet.
> Applications should parse the packet type, and set an exactly correct DEV_TX_OFFLOAD_*_TSO
> flag to gso_types and ol_flags according to the packet type. That is, the value of gso_types
> is on a per-packet basis. Using gso_ctx->gso_types and mbuf->ol_flags at the same time
> is because that DEV_TX_OFFLOAD_*_TSO only tells tunnelling type and the inner L4 type, and
> we need to know L3 type by ol_flags. With this design, HW segmentation and SW segmentation
> are indeed consistent.
> 
> If I understand it correctly, applications need to set 'ol_flags = PKT_TX_IPV4' and
> 'gso_types = DEV_TX_OFFLOAD_VXLAN_TNL_TSO' for a "ether+ipv4+udp+vxlan+ether+ipv4+
> tcp+payload" packet. But PKT_TX_IPV4 just present the inner L3 type for tunneled packet.
> How about the outer L3 type? Always assume the inner and the outer L3 type are the same?

It think that for that case you'll have to set in ol_flags:

PKT_TX_IPV4 | PKT_TX_OUTER_IPV4 | PKT_TX_TUNNEL_VXLAN | PKT_TX_TCP_SEG

Konstantin

> 
> Jiayu
> > Konstantin