[bpf-next V4 PATCH 5/8] xdp: introduce xdp_return_frame_rx_napi

Jesper Dangaard Brouer
2018-05-18T13:35:00Z

When sending an xdp_frame through xdp_do_redirect call, then error
cases can happen where the xdp_frame needs to be dropped, and
returning an -errno code isn't sufficient/possible any-longer
(e.g. for cpumap case). This is already fully supported, by simply
calling xdp_return_frame.

This patch is an optimization, which provides xdp_return_frame_rx_napi,
which is a faster variant for these error cases. It take advantage of
the protection provided by XDP RX running under NAPI protection.

This change is mostly relevant for drivers using the page_pool
allocator as it can take advantage of this. (Tested with mlx5).
---
include/net/page_pool.h | 5 +++--
include/net/xdp.h | 1 +
kernel/bpf/cpumap.c | 2 +-
net/core/xdp.c | 20 ++++++++++++++++----
4 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index c79087153148..694d055e01ef 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -115,13 +115,14 @@ void page_pool_destroy(struct page_pool *pool);
void __page_pool_put_page(struct page_pool *pool,
struct page *page, bool allow_direct);

-static inline void page_pool_put_page(struct page_pool *pool, struct page *page)
+static inline void page_pool_put_page(struct page_pool *pool,
+ struct page *page, bool allow_direct)
{
/* When page_pool isn't compiled-in, net/core/xdp.c doesn't
* allow registering MEM_TYPE_PAGE_POOL, but shield linker.
*/
#ifdef CONFIG_PAGE_POOL
- __page_pool_put_page(pool, page, false);
+ __page_pool_put_page(pool, page, allow_direct);
#endif
}
/* Very limited use-cases allow recycle direct */
diff --git a/include/net/xdp.h b/include/net/xdp.h
index 0b689cf561c7..7ad779237ae8 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -104,6 +104,7 @@ struct xdp_frame *convert_to_xdp_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);

int xdp_rxq_info_reg(struct xdp_rxq_info *xdp_rxq,
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index c95b04ec103e..e0918d180f08 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -578,7 +578,7 @@ static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu,
err = __ptr_ring_produce(q, xdpf);
if (err) {
drops++;
- xdp_return_frame(xdpf);
+ xdp_return_frame_rx_napi(xdpf);
}
processed++;
}
diff --git a/net/core/xdp.c b/net/core/xdp.c
index bf6758f74339..cb8c4e061a5a 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -308,7 +308,13 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
}
EXPORT_SYMBOL_GPL(xdp_rxq_info_reg_mem_model);

-static void xdp_return(void *data, struct xdp_mem_info *mem)
+/* XDP RX runs under NAPI protection, and in different delivery error
+ * scenarios (e.g. queue full), it is possible to return the xdp_frame
+ * while still leveraging this protection. The @napi_direct boolian
+ * is used for those calls sites. Thus, allowing for faster recycling
+ * of xdp_frames/pages in those cases.
+ */
+static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct)
{
struct xdp_mem_allocator *xa;
struct page *page;
@@ -320,7 +326,7 @@ static void xdp_return(void *data, struct xdp_mem_info *mem)
xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
page = virt_to_head_page(data);
if (xa)
- page_pool_put_page(xa->page_pool, page);
+ page_pool_put_page(xa->page_pool, page, napi_direct);
else
put_page(page);
rcu_read_unlock();
@@ -340,12 +346,18 @@ static void xdp_return(void *data, struct xdp_mem_info *mem)

void xdp_return_frame(struct xdp_frame *xdpf)
{
- xdp_return(xdpf->data, &xdpf->mem);
+ __xdp_return(xdpf->data, &xdpf->mem, false);
}
EXPORT_SYMBOL_GPL(xdp_return_frame);

+void xdp_return_frame_rx_napi(struct xdp_frame *xdpf)
+{
+ __xdp_return(xdpf->data, &xdpf->mem, true);
+}
+EXPORT_SYMBOL_GPL(xdp_return_frame_rx_napi);
+
void xdp_return_buff(struct xdp_buff *xdp)
{
- xdp_return(xdp->data, &xdp->rxq->mem);
+ __xdp_return(xdp->data, &xdp->rxq->mem, true);
}
EXPORT_SYMBOL_GPL(xdp_return_buff);