Date:   Wed, 28 Oct 2020 11:27:34 +0200
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        lorenzo.bianconi@...hat.com, davem@...emloft.net, kuba@...nel.org,
        brouer@...hat.com
Subject: Re: [PATCH net-next 1/4] net: xdp: introduce bulking for xdp tx
 return path

Hi Lorenzo,

On Tue, Oct 27, 2020 at 08:04:07PM +0100, Lorenzo Bianconi wrote:
> Introduce bulking capability in xdp tx return path (XDP_REDIRECT).
> xdp_return_frame is usually run inside the driver NAPI tx completion
> loop so it is possible batch it.
> Current implementation considers only page_pool memory model.
> Convert mvneta driver to xdp_return_frame_bulk APIs.
> 
> Suggested-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  drivers/net/ethernet/marvell/mvneta.c |  5 ++-
>  include/net/xdp.h                     |  9 +++++
>  net/core/xdp.c                        | 51 +++++++++++++++++++++++++++
>  3 files changed, 64 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index 54b0bf574c05..43ab8a73900e 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -1834,8 +1834,10 @@ static void mvneta_txq_bufs_free(struct mvneta_port *pp,
>  				 struct netdev_queue *nq, bool napi)
>  {
>  	unsigned int bytes_compl = 0, pkts_compl = 0;
> +	struct xdp_frame_bulk bq;
>  	int i;
>  
> +	bq.xa = NULL;
>  	for (i = 0; i < num; i++) {
>  		struct mvneta_tx_buf *buf = &txq->buf[txq->txq_get_index];
>  		struct mvneta_tx_desc *tx_desc = txq->descs +
> @@ -1857,9 +1859,10 @@ static void mvneta_txq_bufs_free(struct mvneta_port *pp,
>  			if (napi && buf->type == MVNETA_TYPE_XDP_TX)
>  				xdp_return_frame_rx_napi(buf->xdpf);
>  			else
> -				xdp_return_frame(buf->xdpf);
> +				xdp_return_frame_bulk(buf->xdpf, &bq);
>  		}
>  	}
> +	xdp_flush_frame_bulk(&bq);
>  
>  	netdev_tx_completed_queue(nq, pkts_compl, bytes_compl);
>  }
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 3814fb631d52..9567110845ef 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -104,6 +104,12 @@ struct xdp_frame {
>  	struct net_device *dev_rx; /* used by cpumap */
>  };
>  
> +#define XDP_BULK_QUEUE_SIZE	16
> +struct xdp_frame_bulk {
> +	void *q[XDP_BULK_QUEUE_SIZE];
> +	int count;
> +	void *xa;
> +};
>  
>  static inline struct skb_shared_info *
>  xdp_get_shared_info_from_frame(struct xdp_frame *frame)
> @@ -194,6 +200,9 @@ struct xdp_frame *xdp_convert_buff_to_frame(struct xdp_buff *xdp)
>  void xdp_return_frame(struct xdp_frame *xdpf);
>  void xdp_return_frame_rx_napi(struct xdp_frame *xdpf);
>  void xdp_return_buff(struct xdp_buff *xdp);
> +void xdp_flush_frame_bulk(struct xdp_frame_bulk *bq);
> +void xdp_return_frame_bulk(struct xdp_frame *xdpf,
> +			   struct xdp_frame_bulk *bq);
>  
>  /* When sending xdp_frame into the network stack, then there is no
>   * return point callback, which is needed to release e.g. DMA-mapping
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 48aba933a5a8..93eabd789246 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -380,6 +380,57 @@ void xdp_return_frame_rx_napi(struct xdp_frame *xdpf)
>  }
>  EXPORT_SYMBOL_GPL(xdp_return_frame_rx_napi);
>  
> +void xdp_flush_frame_bulk(struct xdp_frame_bulk *bq)
> +{
> +	struct xdp_mem_allocator *xa = bq->xa;
> +	int i;
> +
> +	if (unlikely(!xa))
> +		return;
> +
> +	for (i = 0; i < bq->count; i++) {
> +		struct page *page = virt_to_head_page(bq->q[i]);
> +
> +		page_pool_put_full_page(xa->page_pool, page, false);
> +	}
> +	bq->count = 0;
> +}
> +EXPORT_SYMBOL_GPL(xdp_flush_frame_bulk);
> +
> +void xdp_return_frame_bulk(struct xdp_frame *xdpf,
> +			   struct xdp_frame_bulk *bq)
> +{
> +	struct xdp_mem_info *mem = &xdpf->mem;
> +	struct xdp_mem_allocator *xa, *nxa;
> +
> +	if (mem->type != MEM_TYPE_PAGE_POOL) {
> +		__xdp_return(xdpf->data, &xdpf->mem, false);
> +		return;
> +	}
> +
> +	rcu_read_lock();
> +
> +	xa = bq->xa;
> +	if (unlikely(!xa || mem->id != xa->mem.id)) {

Why is this marked as unlikely? The driver passes it as NULL. Should unlikely be
checked on both xa and the comparison?

> +		nxa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);

Is there a chance nxa can be NULL?

> +		if (unlikely(!xa)) {

Same here, driver passes it as NULL

> +			bq->count = 0;
> +			bq->xa = nxa;
> +			xa = nxa;
> +		}
> +	}
> +
> +	if (mem->id != xa->mem.id || bq->count == XDP_BULK_QUEUE_SIZE)
> +		xdp_flush_frame_bulk(bq);
> +
> +	bq->q[bq->count++] = xdpf->data;
> +	if (mem->id != xa->mem.id)
> +		bq->xa = nxa;
> +
> +	rcu_read_unlock();
> +}
> +EXPORT_SYMBOL_GPL(xdp_return_frame_bulk);
> +
>  void xdp_return_buff(struct xdp_buff *xdp)
>  {
>  	__xdp_return(xdp->data, &xdp->rxq->mem, true);
> -- 
> 2.26.2
> 

Cheers
/Ilias

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