Re: [dpdk-dev] [PATCH 7/9] net/virtio: rationalize setting of Rx/Tx handlers

[Olivier MATZ <olivier.matz@6wind.com>]

Hi Yuanhan,

On Fri, Sep 01, 2017 at 05:19:16PM +0800, Yuanhan Liu wrote:
> On Thu, Aug 31, 2017 at 03:40:13PM +0200, Olivier Matz wrote:
> > The selection of Rx/Tx handlers is done at several places,
> > group them in one function set_rxtx_funcs().
> > 
> > The update of hw->use_simple_rxtx is also rationalized:
> > - initialized to 1 (prefer simple path)
> > - in dev configure or rx/tx queue setup, if something prevents from
> >   using the simple path, change it to 0.
> > - in dev start, set the handlers according to hw->use_simple_rxtx.
> > 
> > Cc: stable@dpdk.org
> 
> This patch looks like a refactoring to me, that I don't think it's really
> a good idea to back port it to a stable release.

I CCed stable for this commit because next ones, which are fixes, depend
on it. If you consider they should not be included in stable, we can also
drop this one.

> ...
> > @@ -1534,7 +1554,6 @@ eth_virtio_dev_init(struct rte_eth_dev *eth_dev)
> >  	RTE_BUILD_BUG_ON(RTE_PKTMBUF_HEADROOM < sizeof(struct virtio_net_hdr_mrg_rxbuf));
> >  
> >  	eth_dev->dev_ops = &virtio_eth_dev_ops;
> > -	eth_dev->tx_pkt_burst = &virtio_xmit_pkts;
> >  
> >  	if (rte_eal_process_type() == RTE_PROC_SECONDARY) {
> >  		if (!hw->virtio_user_dev) {
> > @@ -1544,12 +1563,8 @@ eth_virtio_dev_init(struct rte_eth_dev *eth_dev)
> >  		}
> >  
> >  		virtio_set_vtpci_ops(hw);
> > -		if (hw->use_simple_rxtx) {
> > -			eth_dev->tx_pkt_burst = virtio_xmit_pkts_simple;
> > -			eth_dev->rx_pkt_burst = virtio_recv_pkts_vec;
> > -		} else {
> > -			rx_func_get(eth_dev);
> > -		}
> > +		set_rxtx_funcs(eth_dev);
> 
> No need to invoke it here?

I wanted to stay consistent with previous code.

I'm not very used to work with secondary processes, so I'm not 100% it
is ok, but in my understanding, in that case the configuration is done
first by the primary process, and the secondary the pointers to the
rx/tx funcs. I suppose their value can be different than primary ones.

> 
> > +
> >  		return 0;
> >  	}
> >  
> > @@ -1726,6 +1741,18 @@ virtio_dev_configure(struct rte_eth_dev *dev)
> >  			return -EBUSY;
> >  		}
> >  
> > +	hw->use_simple_rxtx = 1;
> > +
> > +#if defined RTE_ARCH_X86
> > +	if (!rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE3))
> 
> DPDK now requires SSE4.2. You might want to add another patch to remove
> this testing.

ok, will do.

> 
> > +		hw->use_simple_rxtx = 0;
> > +#elif defined RTE_ARCH_ARM64 || defined CONFIG_RTE_ARCH_ARM
> > +	if (!rte_cpu_get_flag_enabled(RTE_CPUFLAG_NEON))
> > +		hw->use_simple_rxtx = 0;
> > +#endif
> > +	if (vtpci_with_feature(hw, VIRTIO_NET_F_MRG_RXBUF))
> > +		hw->use_simple_rxtx = 0;
> > +
> >  	return 0;
> >  }
> >  
> > @@ -1802,6 +1829,7 @@ virtio_dev_start(struct rte_eth_dev *dev)
> >  		VIRTQUEUE_DUMP(txvq->vq);
> >  	}
> >  
> > +	set_rxtx_funcs(dev);
> >  	hw->started = 1;
> >  
> >  	/* Initialize Link state */
> > diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> > index a32e3229f..c9d97b643 100644
> > --- a/drivers/net/virtio/virtio_rxtx.c
> > +++ b/drivers/net/virtio/virtio_rxtx.c
> > @@ -505,25 +505,14 @@ static void
> >  virtio_update_rxtx_handler(struct rte_eth_dev *dev,
> >  			   const struct rte_eth_txconf *tx_conf)
> 
> This function name doesn't quite make sense now after your refactoring.

It updates hw->use_simple_rxtx, which at the end will change the
rxtx handler. I didn't find a better name.

My other (poor) ideas were:
virtio_update_[rxtx_]handler_requirements
virtio_update_[rxtx_]handler_constraints
virtio_update_[rxtx_]handler_selector


> 
> >  {
> > -	uint8_t use_simple_rxtx = 0;
> >  	struct virtio_hw *hw = dev->data->dev_private;
> > +	uint8_t use_simple_rxtx = hw->use_simple_rxtx;
> >  
> > -#if defined RTE_ARCH_X86
> > -	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE3))
> > -		use_simple_rxtx = 1;
> > -#elif defined RTE_ARCH_ARM64 || defined CONFIG_RTE_ARCH_ARM
> > -	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_NEON))
> > -		use_simple_rxtx = 1;
> > -#endif
> > -	/* Use simple rx/tx func if single segment and no offloads */
> > -	if (use_simple_rxtx &&
> > -	    (tx_conf->txq_flags & VIRTIO_SIMPLE_FLAGS) == VIRTIO_SIMPLE_FLAGS &&
> > -	    !vtpci_with_feature(hw, VIRTIO_NET_F_MRG_RXBUF)) {
> > -		PMD_INIT_LOG(INFO, "Using simple rx/tx path");
> > -		dev->tx_pkt_burst = virtio_xmit_pkts_simple;
> > -		dev->rx_pkt_burst = virtio_recv_pkts_vec;
> > -		hw->use_simple_rxtx = use_simple_rxtx;
> > -	}
> > +	/* cannot use simple rxtx funcs with multisegs or offloads */
> > +	if ((tx_conf->txq_flags & VIRTIO_SIMPLE_FLAGS) != VIRTIO_SIMPLE_FLAGS)
> > +		use_simple_rxtx = 0;
> 
> And that's what left in this function. How about just un-folding it?
> 
> 	--yliu

yep, we can inline it.