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Date: Wed, 4 Nov 2020 12:11:58 +0100
From: Jesper Dangaard Brouer <brouer@...hat.com>
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,
ilias.apalodimas@...aro.org, brouer@...hat.com,
Ioana Ciornei <ioana.ciornei@....com>,
Ioana Radulescu <ruxandra.radulescu@....com>
Subject: Re: [PATCH v3 net-next 1/5] net: xdp: introduce bulking for xdp tx
return path
On Wed, 4 Nov 2020 11:22:54 +0100
Lorenzo Bianconi <lorenzo@...nel.org> 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>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
> include/net/xdp.h | 9 +++++++
> net/core/xdp.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 70 insertions(+)
>
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 3814fb631d52..a1f48a73e6df 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 {
> + int count;
> + void *xa;
> + void *q[XDP_BULK_QUEUE_SIZE];
> +};
>
> 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..66ac275a0360 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -380,6 +380,67 @@ 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
If this is connected, then why have you not redefined DEV_MAP_BULK_SIZE?
Cc. DPAA2 maintainers as they use this define in their drivers.
You want to make sure this driver is flexible enough for future changes.
Like:
diff --git a/include/net/xdp.h b/include/net/xdp.h
index 3814fb631d52..44440a36f96f 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -245,6 +245,6 @@ 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__ */
> + * 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->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;
> +
> + if (mem->type != MEM_TYPE_PAGE_POOL) {
> + __xdp_return(xdpf->data, &xdpf->mem, false);
> + return;
> + }
>
I cannot make up my mind: It would be a micro-optimization to move
this if-statement to include/net/xdp.h, but it will make code harder to
read/follow, and the call you replace xdp_return_frame() is also in
xdp.c with same call to _xdp_return(). Let keep it as-is. (we can
followup with micro-optimizations)
> + rcu_read_lock();
> +
> + 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 (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;
> +
> + 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);
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
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