netdev - Re: [PATCH v6 net-nex 1/5] net: xdp: introduce bulking for xdp tx return path

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Date:   Fri, 13 Nov 2020 22:58:23 +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, john.fastabend@...il.com
Subject: Re: [PATCH v6 net-nex 1/5] net: xdp: introduce bulking for xdp tx
 return path

On Fri, Nov 13, 2020 at 12:48:28PM +0100, Lorenzo Bianconi wrote:
> XDP bulk APIs introduce a defer/flush mechanism to return
> pages belonging to the same xdp_mem_allocator object
> (identified via the mem.id field) in bulk to optimize
> I-cache and D-cache since xdp_return_frame is usually run
> inside the driver NAPI tx completion loop.
> The bulk queue size is set to 16 to be aligned to how
> XDP_REDIRECT bulking works. The bulk is flushed when
> it is full or when mem.id changes.
> xdp_frame_bulk is usually stored/allocated on the function
> call-stack to avoid locking penalties.
> Current implementation considers only page_pool memory model.
> 
> Suggested-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Co-developed-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  include/net/xdp.h | 17 +++++++++++++-
>  net/core/xdp.c    | 59 +++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 75 insertions(+), 1 deletion(-)
> 
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 3814fb631d52..7d48b2ae217a 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -104,6 +104,18 @@ struct xdp_frame {
>  	struct net_device *dev_rx; /* used by cpumap */
>  };
>  
> +#define XDP_BULK_QUEUE_SIZE	16
> +struct xdp_frame_bulk {
> +	int count;
> +	void *xa;
> +	void *q[XDP_BULK_QUEUE_SIZE];
> +};
> +
> +static __always_inline void xdp_frame_bulk_init(struct xdp_frame_bulk *bq)
> +{
> +	/* bq->count will be zero'ed when bq->xa gets updated */
> +	bq->xa = NULL;
> +}
>  
>  static inline struct skb_shared_info *
>  xdp_get_shared_info_from_frame(struct xdp_frame *frame)
> @@ -194,6 +206,9 @@ 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
> @@ -245,6 +260,6 @@ bool xdp_attachment_flags_ok(struct xdp_attachment_info *info,
>  void xdp_attachment_setup(struct xdp_attachment_info *info,
>  			  struct netdev_bpf *bpf);
>  
> -#define DEV_MAP_BULK_SIZE 16
> +#define DEV_MAP_BULK_SIZE XDP_BULK_QUEUE_SIZE
>  
>  #endif /* __LINUX_NET_XDP_H__ */
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 48aba933a5a8..bbaee7fdd44f 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -380,6 +380,65 @@ void xdp_return_frame_rx_napi(struct xdp_frame *xdpf)
>  }
>  EXPORT_SYMBOL_GPL(xdp_return_frame_rx_napi);
>  
> +/* XDP bulk APIs introduce a defer/flush mechanism to return
> + * pages belonging to the same xdp_mem_allocator object
> + * (identified via the mem.id field) in bulk to optimize
> + * I-cache and D-cache.
> + * The bulk queue size is set to 16 to be aligned to how
> + * XDP_REDIRECT bulking works. The bulk is flushed when
> + * it is full or when mem.id changes.
> + * xdp_frame_bulk is usually stored/allocated on the function
> + * call-stack to avoid locking penalties.
> + */
> +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->xa is not cleared to save lookup, if mem.id same in next bulk */
> +	bq->count = 0;
> +}
> +EXPORT_SYMBOL_GPL(xdp_flush_frame_bulk);
> +
> +/* Must be called with rcu_read_lock held */
> +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;
> +
> +	if (mem->type != MEM_TYPE_PAGE_POOL) {
> +		__xdp_return(xdpf->data, &xdpf->mem, false);
> +		return;
> +	}
> +
> +	xa = bq->xa;
> +	if (unlikely(!xa)) {
> +		xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> +		bq->count = 0;
> +		bq->xa = xa;
> +	}
> +
> +	if (bq->count == XDP_BULK_QUEUE_SIZE)
> +		xdp_flush_frame_bulk(bq);
> +
> +	if (unlikely(mem->id != xa->mem.id)) {
> +		xdp_flush_frame_bulk(bq);
> +		bq->xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> +	}
> +
> +	bq->q[bq->count++] = xdpf->data;
> +}
> +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
> 

Could you add the changes in the Documentation as well (which can do in later)

Acked-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>