Re: [PATCH v3 net-next 8/8] net: mvneta: add XDP_TX support

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

On Wed, Oct 16, 2019 at 12:09:00PM +0200, Lorenzo Bianconi wrote:
> > On Mon, 14 Oct 2019 12:49:55 +0200, Lorenzo Bianconi wrote:
> > > Implement XDP_TX verdict and ndo_xdp_xmit net_device_ops function
> > > pointer
> > > 
> > > Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> > 
> > > @@ -1972,6 +1975,109 @@ int mvneta_rx_refill_queue(struct mvneta_port *pp, struct mvneta_rx_queue *rxq)
> > >  	return i;
> > >  }
> > >  
> > > +static int
> > > +mvneta_xdp_submit_frame(struct mvneta_port *pp, struct mvneta_tx_queue *txq,
> > > +			struct xdp_frame *xdpf, bool dma_map)
> > > +{
> > > +	struct mvneta_tx_desc *tx_desc;
> > > +	struct mvneta_tx_buf *buf;
> > > +	dma_addr_t dma_addr;
> > > +
> > > +	if (txq->count >= txq->tx_stop_threshold)
> > > +		return MVNETA_XDP_CONSUMED;
> > > +
> > > +	tx_desc = mvneta_txq_next_desc_get(txq);
> > > +
> > > +	buf = &txq->buf[txq->txq_put_index];
> > > +	if (dma_map) {
> > > +		/* ndo_xdp_xmit */
> > > +		dma_addr = dma_map_single(pp->dev->dev.parent, xdpf->data,
> > > +					  xdpf->len, DMA_TO_DEVICE);
> > > +		if (dma_mapping_error(pp->dev->dev.parent, dma_addr)) {
> > > +			mvneta_txq_desc_put(txq);
> > > +			return MVNETA_XDP_CONSUMED;
> > > +		}
> > > +		buf->type = MVNETA_TYPE_XDP_NDO;
> > > +	} else {
> > > +		struct page *page = virt_to_page(xdpf->data);
> > > +
> > > +		dma_addr = page_pool_get_dma_addr(page) +
> > > +			   pp->rx_offset_correction + MVNETA_MH_SIZE;
> > > +		dma_sync_single_for_device(pp->dev->dev.parent, dma_addr,
> > > +					   xdpf->len, DMA_BIDIRECTIONAL);
> > 
> > This looks a little suspicious, XDP could have moved the start of frame
> > with adjust_head, right? You should also use xdpf->data to find where
> > the frame starts, no?
> 
> uhm, right..we need to update the dma_addr doing something like:
> 
> dma_addr = page_pool_get_dma_addr(page) + xdpf->data - xdpf;

Can we do  page_pool_get_dma_addr(page) + xdpf->headroom as well right?

> 
> and then use xdpf->len for dma-sync
> 
> > 
> > > +		buf->type = MVNETA_TYPE_XDP_TX;
> > > +	}
> > > +	buf->xdpf = xdpf;
> > > +
> > > +	tx_desc->command = MVNETA_TXD_FLZ_DESC;
> > > +	tx_desc->buf_phys_addr = dma_addr;
> > > +	tx_desc->data_size = xdpf->len;
> > > +
> > > +	mvneta_update_stats(pp, 1, xdpf->len, true);
> > > +	mvneta_txq_inc_put(txq);
> > > +	txq->pending++;
> > > +	txq->count++;
> > > +
> > > +	return MVNETA_XDP_TX;
> > > +}
> > > +
> > > +static int
> > > +mvneta_xdp_xmit_back(struct mvneta_port *pp, struct xdp_buff *xdp)
> > > +{
> > > +	struct xdp_frame *xdpf = convert_to_xdp_frame(xdp);
> > > +	int cpu = smp_processor_id();
> > > +	struct mvneta_tx_queue *txq;
> > > +	struct netdev_queue *nq;
> > > +	u32 ret;
> > > +
> > > +	if (unlikely(!xdpf))
> > > +		return MVNETA_XDP_CONSUMED;
> > 
> > Personally I'd prefer you haven't called a function which return code
> > has to be error checked in local variable init.
> 
> do you mean moving cpu = smp_processor_id(); after the if condition?
> 
> Regards,
> Lorenzo
> 
> > 
> > > +
> > > +	txq = &pp->txqs[cpu % txq_number];
> > > +	nq = netdev_get_tx_queue(pp->dev, txq->id);
> > > +
> > > +	__netif_tx_lock(nq, cpu);
> > > +	ret = mvneta_xdp_submit_frame(pp, txq, xdpf, false);
> > > +	if (ret == MVNETA_XDP_TX)
> > > +		mvneta_txq_pend_desc_add(pp, txq, 0);
> > > +	__netif_tx_unlock(nq);
> > > +
> > > +	return ret;
> > > +}

Thanks
/Ilias