Subject: Re: [PATCH v4 net-next 2/7] net: mvneta: introduce page pool API for sw buffer manager

From: Lorenzo Bianconi <[email-masked]>
Date: Thu, 17 Oct 2019 11:58:40 +0200

> On Wed, 16 Oct 2019 23:03:07 +0200, Lorenzo Bianconi wrote:

[...]

> >  
> > @@ -1894,10 +1893,11 @@ static void mvneta_rxq_drop_pkts(struct mvneta_port *pp,
> >  		if (!data || !(rx_desc->buf_phys_addr))
> >  			continue;
> >  
> > -		dma_unmap_page(pp->dev->dev.parent, rx_desc->buf_phys_addr,
> > -			       PAGE_SIZE, DMA_FROM_DEVICE);
> > -		__free_page(data);
> > +		page_pool_put_page(rxq->page_pool, data, false);
> >  	}
> > +	if (xdp_rxq_info_is_reg(&rxq->xdp_rxq))
> > +		xdp_rxq_info_unreg(&rxq->xdp_rxq);
> > +	page_pool_destroy(rxq->page_pool);
> 
> I think you may need to set the page_pool pointer to NULL here, no?
> AFAICT the ndo_stop in this driver has to be idempotent due to the
> open/close-to-reconfigure dances.
> 
> >  }
> >  
> >  static void
> > @@ -2029,8 +2029,7 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
> >  				skb_add_rx_frag(rxq->skb, frag_num, page,
> >  						frag_offset, frag_size,
> >  						PAGE_SIZE);
> > -				dma_unmap_page(dev->dev.parent, phys_addr,
> > -					       PAGE_SIZE, DMA_FROM_DEVICE);
> > +				page_pool_release_page(rxq->page_pool, page);
> >  				rxq->left_size -= frag_size;
> >  			}
> >  		} else {
> > @@ -2060,9 +2059,7 @@ static int mvneta_rx_swbm(struct napi_struct *napi,
> >  						frag_offset, frag_size,
> >  						PAGE_SIZE);
> >  
> > -				dma_unmap_page(dev->dev.parent, phys_addr,
> > -					       PAGE_SIZE, DMA_FROM_DEVICE);
> > -
> > +				page_pool_release_page(rxq->page_pool, page);
> >  				rxq->left_size -= frag_size;
> >  			}
> >  		} /* Middle or Last descriptor */
> > @@ -2829,11 +2826,53 @@ static int mvneta_poll(struct napi_struct *napi, int budget)
> >  	return rx_done;
> >  }
> >  
> > +static int mvneta_create_page_pool(struct mvneta_port *pp,
> > +				   struct mvneta_rx_queue *rxq, int size)
> > +{
> > +	struct page_pool_params pp_params = {
> > +		.order = 0,
> > +		.flags = PP_FLAG_DMA_MAP,
> > +		.pool_size = size,
> > +		.nid = cpu_to_node(0),
> > +		.dev = pp->dev->dev.parent,
> > +		.dma_dir = DMA_FROM_DEVICE,
> > +	};
> > +	int err;
> > +
> > +	rxq->page_pool = page_pool_create(&pp_params);
> > +	if (IS_ERR(rxq->page_pool)) {
> > +		err = PTR_ERR(rxq->page_pool);
> > +		rxq->page_pool = NULL;
> > +		return err;
> > +	}
> > +
> > +	err = xdp_rxq_info_reg(&rxq->xdp_rxq, pp->dev, rxq->id);
> > +	if (err < 0)
> > +		goto err_free_pp;
> > +
> > +	err = xdp_rxq_info_reg_mem_model(&rxq->xdp_rxq, MEM_TYPE_PAGE_POOL,
> > +					 rxq->page_pool);
> > +	if (err)
> > +		goto err_unregister_rxq;
> > +
> > +	return 0;
> > +
> > +err_unregister_rxq:
> > +	xdp_rxq_info_unreg(&rxq->xdp_rxq);
> > +err_free_pp:
> > +	page_pool_destroy(rxq->page_pool);
> 
> ditto
> 
> > +	return err;
> > +}
> > +
> >  /* Handle rxq fill: allocates rxq skbs; called when initializing a port */
> >  static int mvneta_rxq_fill(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
> >  			   int num)
> >  {
> > -	int i;
> > +	int i, err;
> > +
> > +	err = mvneta_create_page_pool(pp, rxq, num);
> > +	if (err < 0)
> > +		return err;
> 
> Note that callers of mvneta_rxq_fill() never check the return code.
> Some form of error print or such could be justified here.. although
> actually propagating the error code all the way back to user space is
> even better.

ack, I agree. I will add a dedicated patch in the series.

> 
> IMHO on device start the fill ring should be required to be filled up
> completely, but that's just an opinion.

at bootstrap mvneta_rxq_fill() is run with num set to rxq->size so I guess to
the max allowed value (512 by default)

Regards,
Lorenzo

> 
> >  	for (i = 0; i < num; i++) {
> >  		memset(rxq->descs + i, 0, sizeof(struct mvneta_rx_desc));