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From: "Rong, Leyi" <leyi.rong@intel.com>
To: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>,
	"Zhang, Qi Z" <qi.z.zhang@intel.com>,
	"Xing, Beilei" <beilei.xing@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] net/i40e: add Tx preparation for vector data path
Date: Tue, 13 Apr 2021 10:23:40 +0000	[thread overview]
Message-ID: <SN6PR11MB262173C2F1DBDBEB2083576BEC4F9@SN6PR11MB2621.namprd11.prod.outlook.com> (raw)
In-Reply-To: <DM6PR11MB4491CC5FB58DD90450E2FEE79A739@DM6PR11MB4491.namprd11.prod.outlook.com>


> -----Original Message-----
> From: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> Sent: Friday, April 9, 2021 6:40 PM
> To: Rong, Leyi <leyi.rong@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>;
> Zhang, Qi Z <qi.z.zhang@intel.com>; Xing, Beilei <beilei.xing@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.rong@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.

  reply	other threads:[~2021-04-13 10:23 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-31  8:53 Leyi Rong
2021-04-01 12:27 ` Zhang, Qi Z
2021-04-01 12:33 ` David Marchand
2021-04-01 13:19   ` Ananyev, Konstantin
2021-04-07 16:39 ` Ferruh Yigit
2021-04-08  8:29   ` Rong, Leyi
2021-04-08 10:32     ` Ananyev, Konstantin
2021-04-09  7:19       ` Rong, Leyi
2021-04-09 10:40         ` Ananyev, Konstantin
2021-04-13 10:23           ` Rong, Leyi [this message]
2021-04-13 10:41             ` Ananyev, Konstantin
2021-04-08  8:39   ` David Marchand
2021-04-08  8:49     ` Rong, Leyi
2021-04-19  8:36 ` [dpdk-dev] [PATCH v2] net/i40e: add Tx preparation for simple Tx " Leyi Rong
2021-04-19  9:36   ` Zhang, Qi Z
2021-04-19 10:59   ` Ananyev, Konstantin
2021-04-20  5:31     ` Rong, Leyi
2021-04-20  5:29 ` [dpdk-dev] [PATCH v3] " Leyi Rong
2021-04-20  8:03   ` Ananyev, Konstantin
2021-04-20 14:00     ` Zhang, Qi Z

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