> -----Original Message-----
> From: Ananyev, Konstantin <konstantin.anan...@intel.com>
> Sent: Friday, April 9, 2021 6:40 PM
> To: Rong, Leyi <leyi.r...@intel.com>; Yigit, Ferruh <ferruh.yi...@intel.com>;
> Zhang, Qi Z <qi.z.zh...@intel.com>; Xing, Beilei <beilei.x...@intel.com>
> Cc: dev@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH] net/i40e: add Tx preparation for vector data
> path
>
>
>
> > > > > > Fill up dev->tx_pkt_prepare to i40e_pkt_prepare when on vector
> > > > > > and simple data path selection, as the sanity check is needed
> > > > > > ideally.
> > > > > >
> > > > > > Signed-off-by: Leyi Rong <leyi.r...@intel.com>
> > > > > > ---
> > > > > > drivers/net/i40e/i40e_rxtx.c | 2 +-
> > > > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/drivers/net/i40e/i40e_rxtx.c
> > > > > > b/drivers/net/i40e/i40e_rxtx.c index 61cb204be2..b3d7765e3b
> > > > > > 100644
> > > > > > --- a/drivers/net/i40e/i40e_rxtx.c
> > > > > > +++ b/drivers/net/i40e/i40e_rxtx.c
> > > > > > @@ -3412,7 +3412,7 @@ i40e_set_tx_function(struct rte_eth_dev
> *dev)
> > > > > > PMD_INIT_LOG(DEBUG, "Simple tx finally be
> used.");
> > > > > > dev->tx_pkt_burst = i40e_xmit_pkts_simple;
> > > > > > }
> > > > > > - dev->tx_pkt_prepare = NULL;
> > > > > > + dev->tx_pkt_prepare = i40e_prep_pkts;
> > > > > > } else {
> > > > > > PMD_INIT_LOG(DEBUG, "Xmit tx finally be used.");
> > > > > > dev->tx_pkt_burst = i40e_xmit_pkts;
> > > > > >
> > > > >
> > > > > It seems prepare function is doing some sanity checks before
> > > > > handing packets to the HW.
> > > > > So with this change all Tx paths calls the same Tx prepare
> > > > > function, if so why not set the function pointer outside of the
> > > > > if block, instead of setting it in both legs of the if/else?
> > > > > This clarifies that Tx prepare
> > > used always.
> > > >
> > > > Hi Ferruh,
> > > >
> > > > Yes, it make sense.
> > > >
> > > > Hi Konstantin,
> > >
> > > Hi Leyi,
> > >
> > > >
> > > > Would that be something wrong if the prepare function goes for
> > > > simple Tx
> > > function although it does not support the offload feature yet?
> > > >
> > >
> > > Current situation:
> > > For simple TX path we set dev->tx_pkt_prepare = NULL.
> > > That makes rte_eth_tx_prepare() a stub that does nothing and always
> returns:
> > > "All packets are good".
> > > That is unsafe off-course, and if upper layer will pass a packet
> > > that is not supported, then it can lead to various bad things: bad
> > > cksum, corrupted packets, TX hang, etc.
> > > But at least it keeps simple TX path fast.
> > > With that patch:
> > > For simple TX path we set dev->tx_pkt_prepare = i40e_prep_pkts.
> > > Now on TX path we invoke extra function that does a lot of checks,
> > > but it still
> > > unsafe:
> > > as i40e_prep_pkts() assumes that full-featured TX function is in
> > > place (multi-segs are allowed, etc.).
> > > So our simple TX path became slower, but still is unsafe.
> > > I think that if we want to introduce tx_prepare() for simple TX
> > > path, then the proper way - create a new function for it
> (i40e_simple_prep_pkts() or so).
> > > It will be aware that simple TX path is in place and more
> > > restrictions should be
> > > met:
> > > check that nb_segs==1 and no TX offloads (except FAST_FREE?) are
> > > enabled, plus usual checks for min and max pkt_len.
> > >
> > > Konstantin
> > >
>
>
> Hi Leyi,
>
> > Hi Konstantin,
> >
> > Thanks for the explanation, I know the current full-featured prepare
> > function will cost more CPU cycle, but not sure how to say is still unsafe?
>
> Let say user will do:
>
> mb = create_and_fill_multi_seg_pkt(...);
> n = rte_eth_tx_prepare(p, q, &mb, 1);
> if (n == 1)
> n = rte_eth_tx_burst(p, q, &mb, 1);
> else
> rte_pktmbuf_free(mb);
>
> if dev->tx_pkt_prepare == i40e_prep_pkts and dev->tx_pkt_burs ==
> i40e_xmit_pkts_simple, then this code will TX the packet, even though it
> shouldn't in theory.
>
Hi Konstantin,
Yes, it make sense for the current situation.
> > Why I set the simple Tx prepare function to the current
> > i40e_prep_pkts() is we may support more offload features like current full-
> featured Tx for vector path(which is included in simple Tx currently), if so,
> the
> current tx prepare function can be re-used.
>
> AFAIK, for i40e current simple (and vector) TX path doesn't support all
> offloads
> that are supported by full-featured path To be more specific: mulit-seg
> packets,
> TCP_CKSUM, TCP_SEG, etc.
> Am I missing something obvious here?
>
> Konstantin
We're intending to support more offload features into vector path gradually,
ice/iavf PMD will support Tx checksum offload in AVX512 path in the 2105
release, also will try to support more in the future if possible.
