Re: [dpdk-stable] [PATCH 19.11 6/6] net/mlx5: fix multi-segment inline for the first segments

[Bing Zhao <bingz@nvidia.com>]

Hi Christian,

I talked with Slava, some feature is not supported in LTS 19.11. So please discard this commit.
And I sent a v2 to reply the original email thread.

Thanks

> -----Original Message-----
> From: Christian Ehrhardt <christian.ehrhardt@canonical.com>
> Sent: Tuesday, August 17, 2021 7:55 PM
> To: Bing Zhao <bingz@nvidia.com>
> Cc: dpdk stable <stable@dpdk.org>; Slava Ovsiienko
> <viacheslavo@nvidia.com>; Matan Azrad <matan@nvidia.com>
> Subject: Re: [PATCH 19.11 6/6] net/mlx5: fix multi-segment inline
> for the first segments
> 
> External email: Use caution opening links or attachments
> 
> 
> On Mon, Aug 16, 2021 at 6:30 PM Bing Zhao <bingz@nvidia.com> wrote:
> >
> > From: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
> >
> > [ upstream commit ec837ad0fc7c6df4912cc2706b9cd54b225f4a34 ]
> 
> While not applying this causes build fails on some platforms.
> 
> Looks like:
> [  974s] ../drivers/net/mlx5/mlx5_rxtx.c: In function
> ‘mlx5_tx_packet_multi_inline’:
> [  974s] ../drivers/net/mlx5/mlx5_rxtx.c:3356:31: error:
> ‘PKT_TX_DYNF_NOINLINE’ undeclared (first use in this function)
> [  974s]  3356 |   } else if (mbuf->ol_flags & PKT_TX_DYNF_NOINLINE
> ||
> [  974s]       |                               ^~~~~~~~~~~~~~~~~~~~
> [  974s] ../drivers/net/mlx5/mlx5_rxtx.c:3356:31: note: each
> undeclared identifier is reported only once for each function it
> appears in [  974s] ninja: build stopped: subcommand failed.
> 
> And indeed this is the only occurrence
> 
> $ grep -Hrn PKT_TX_DYNF_NOINLINE *
> drivers/net/mlx5/mlx5_rxtx.c:3356: } else if (mbuf->ol_flags &
> PKT_TX_DYNF_NOINLINE ||
> 
> Since it only happens on some releases I'd assume the other
> arch/distros just do not build this?
> It seems to only affect those building with meson.
> 
> For now I've removed this patch again from 19.11 - please have a
> look and let me know if you'll provide a refreshed backport.
> 
> 
> 
> > Before 19.08 release the Tx burst routines of mlx5 PMD provided
> data
> > inline for the first short segments of the multi-segment packets.
> In
> > the release 19.08 mlx5 Tx datapath was refactored and this
> behavior
> > was broken, affecting the performance.
> >
> > For example, the T-Rex traffic generator might use small leading
> > segments to handle packet headers and performance degradation was
> > noticed.
> >
> > If the first segments of the multi-segment packet are short and
> the
> > overall length is below the inline threshold it should be inline
> into
> > the WQE to fix the performance.
> >
> > Fixes: 18a1c20044c0 ("net/mlx5: implement Tx burst template")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
> > Signed-off-by: Bing Zhao <bingz@nvidia.com>
> > ---
> >  drivers/net/mlx5/mlx5_rxtx.c | 27 +++++++++++++--------------
> >  1 file changed, 13 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/net/mlx5/mlx5_rxtx.c
> > b/drivers/net/mlx5/mlx5_rxtx.c index 73dbf68d2b..094e359e55 100644
> > --- a/drivers/net/mlx5/mlx5_rxtx.c
> > +++ b/drivers/net/mlx5/mlx5_rxtx.c
> > @@ -3336,6 +3336,8 @@ mlx5_tx_packet_multi_inline(struct
> mlx5_txq_data *restrict txq,
> >                 unsigned int nxlen;
> >                 uintptr_t start;
> >
> > +               mbuf = loc->mbuf;
> > +               nxlen = rte_pktmbuf_data_len(mbuf);
> >                 /*
> >                  * Packet length exceeds the allowed inline
> >                  * data length, check whether the minimal @@ -
> 3345,27
> > +3347,23 @@ mlx5_tx_packet_multi_inline(struct mlx5_txq_data
> *restrict txq,
> >                         assert(txq->inlen_mode >=
> MLX5_ESEG_MIN_INLINE_SIZE);
> >                         assert(txq->inlen_mode <= txq->inlen_send);
> >                         inlen = txq->inlen_mode;
> > -               } else {
> > -                       if (!vlan || txq->vlan_en) {
> > -                               /*
> > -                                * VLAN insertion will be done
> inside by HW.
> > -                                * It is not utmost effective -
> VLAN flag is
> > -                                * checked twice, but we should
> proceed the
> > -                                * inlining length correctly and
> take into
> > -                                * account the VLAN header being
> inserted.
> > -                                */
> > -                               return mlx5_tx_packet_multi_send
> > -                                                       (txq, loc,
> olx);
> > -                       }
> > +               } else if (vlan && !txq->vlan_en) {
> > +                       /*
> > +                        * VLAN insertion is requested and
> hardware does not
> > +                        * support the offload, will do with
> software inline.
> > +                        */
> >                         inlen = MLX5_ESEG_MIN_INLINE_SIZE;
> > +               } else if (mbuf->ol_flags & PKT_TX_DYNF_NOINLINE
> ||
> > +                          nxlen > txq->inlen_send) {
> > +                       return mlx5_tx_packet_multi_send(txq, loc,
> olx);
> > +               } else {
> > +                       goto do_first;
> >                 }
> >                 /*
> >                  * Now we know the minimal amount of data is
> requested
> >                  * to inline. Check whether we should inline the
> buffers
> >                  * from the chain beginning to eliminate some
> mbufs.
> >                  */
> > -               mbuf = loc->mbuf;
> > -               nxlen = rte_pktmbuf_data_len(mbuf);
> >                 if (unlikely(nxlen <= txq->inlen_send)) {
> >                         /* We can inline first mbuf at least. */
> >                         if (nxlen < inlen) { @@ -3387,6 +3385,7 @@
> > mlx5_tx_packet_multi_inline(struct mlx5_txq_data *restrict txq,
> >                                         goto do_align;
> >                                 }
> >                         }
> > +do_first:
> >                         do {
> >                                 inlen = nxlen;
> >                                 mbuf = NEXT(mbuf);
> > --
> > 2.21.0
> >
> 
> 
> --
> Christian Ehrhardt
> Staff Engineer, Ubuntu Server
> Canonical Ltd