[dpdk-dev] [PATCH v2 1/3] virtio: conditional compilation cleanup

[Yuanhan Liu]

On Mon, Jul 04, 2016 at 05:45:57PM +0530, Jerin Jacob wrote:
> On Mon, Jul 04, 2016 at 07:02:25PM +0800, Yuanhan Liu wrote:
> > On Mon, Jul 04, 2016 at 02:37:55PM +0530, Jerin Jacob wrote:
> > > On Mon, Jul 04, 2016 at 04:42:32PM +0800, Yuanhan Liu wrote:
> > > > On Mon, Jul 04, 2016 at 02:06:27PM +0530, Jerin Jacob wrote:
> > > > > On Mon, Jul 04, 2016 at 03:36:48PM +0800, Yuanhan Liu wrote:
> > > > > > On Fri, Jul 01, 2016 at 04:46:36PM +0530, Jerin Jacob wrote:
> > > > > > > @@ -494,9 +486,6 @@ virtio_dev_tx_queue_setup(struct rte_eth_dev *dev,
> > > > > > >  {
> > > > > > >  	uint8_t vtpci_queue_idx = 2 * queue_idx + VTNET_SQ_TQ_QUEUE_IDX;
> > > > > > >  
> > > > > > > -#ifdef RTE_MACHINE_CPUFLAG_SSSE3
> > > > > > > -	struct virtio_hw *hw = dev->data->dev_private;
> > > > > > > -#endif
> > > > > > >  	struct virtnet_tx *txvq;
> > > > > > >  	struct virtqueue *vq;
> > > > > > >  	uint16_t tx_free_thresh;
> > > > > > > @@ -511,13 +500,14 @@ virtio_dev_tx_queue_setup(struct rte_eth_dev *dev,
> > > > > > >  	}
> > > > > > >  
> > > > > > >  #ifdef RTE_MACHINE_CPUFLAG_SSSE3
> > > > > > > +	struct virtio_hw *hw = dev->data->dev_private;
> > > > > > 
> > > > > > I'd suggest to move above declaration to ...
> > > > > > 
> > > > > > >  	/* Use simple rx/tx func if single segment and no offloads */
> > > > > > >  	if ((tx_conf->txq_flags & VIRTIO_SIMPLE_FLAGS) == VIRTIO_SIMPLE_FLAGS &&
> > > > > > >  	     !vtpci_with_feature(hw, VIRTIO_NET_F_MRG_RXBUF)) {
> > > > > > 
> > > > > > here: we should try to avoid declaring vars in the middle of a code block.
> > > > > 
> > > > > Next patch in this series, moving all rxtx handler selection code to
> > > > > separate function(virtio_update_rxtx_handler()) where declaration comes
> > > > > as first line in the function.i.e the comment is taken care of in the
> > > > > series.
> > > > 
> > > > Yes, I saw that. But in principle, each patch is atomic: it's not a
> > > > good idea/practice to introduce issues in path A and then fix it in
> > > > path B.
> > > 
> > > In my view it was not an issue as I was removing all possible
> > > conditional compilation flag. If I were to move the declaration to top
> > > then another conditional compilation RTE_MACHINE_CPUFLAG_SSSE3
> > > flag I need to add around declaring the variable.
> > 
> > Nope, I was suggesting to move it inside the "if" block. So, this
> > is actually consistent with what you are trying to do. Besides, it
> > removes an declaration in the middle.
> 
> Just to get the clarity on "moving inside the 'if' block"
> 
> Are you suggesting to have like below?
> 
>  #ifdef RTE_MACHINE_CPUFLAG_SSSE3
> +       struct virtio_hw *hw;
>         /* Use simple rx/tx func if single segment and no offloads */
>         if ((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;
> -               use_simple_rxtx = 1;
> +		hw = dev->data->dev_private;
> +               hw->use_simple_rxtx = 1;
>         }
>  #endif
> 
> 
> Instead of following scheme in existing patch,
> 
>  #ifdef RTE_MACHINE_CPUFLAG_SSSE3
> +       struct virtio_hw *hw = dev->data->dev_private;
>         /* Use simple rx/tx func if single segment and no offloads */
>         if ((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;
> -               use_simple_rxtx = 1;
> +               hw->use_simple_rxtx = 1;
>         }
>  #endif
> 
> 
> The former case will have issue as "hw" been used in "if" with vtpci_with_feature.

Oh, my bad. I overlooked it. Sorry for that!

> OR
> 
> if you meant just floating "struct virtio_hw *hw" without RTE_MACHINE_CPUFLAG_SSSE3
> then it comes error on non x86 as unused "hw" variable.
> 
> If you meant something else then let me know?

I then prefer to keep the "#ifdef .. #endif" on top then. It will stop
us from offending a minor rule, while you can remove the ugly "#ifdef"
block in the next patch.

Works to you?

	--yliu