[PATCH bpf-next 5/9] bpf: cpumap: reuse skb array instead of a linked list to chain skbs

[Alexander Lobakin <aleksander.lobakin@intel.com>]

cpumap still uses linked lists to store a list of skbs to pass to the
stack. Now that we don't use listified Rx in favor of
napi_gro_receive(), linked list is now an unneeded overhead.
Inside the polling loop, we already have an array of skbs. Let's reuse
it for skbs passed to cpumap (generic XDP) and use napi_gro_receive()
directly in case of XDP_PASS when a program is installed to the map
itself. Don't list regular xdp_frames at all and just call
napi_gro_receive() directly as well right after building an skb.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
---
 kernel/bpf/cpumap.c | 55 +++++++++++++++++++++------------------------
 1 file changed, 26 insertions(+), 29 deletions(-)

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index d1cfa4111727..d7206f3f6e80 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -150,21 +150,23 @@ static void __cpu_map_ring_cleanup(struct ptr_ring *ring)
 }
 
 static void cpu_map_bpf_prog_run_skb(struct bpf_cpu_map_entry *rcpu,
-				     struct list_head *listp,
+				     void **skbs, u32 skb_n,
 				     struct xdp_cpumap_stats *stats)
 {
-	struct sk_buff *skb, *tmp;
 	struct xdp_buff xdp;
 	u32 act;
 	int err;
 
-	list_for_each_entry_safe(skb, tmp, listp, list) {
+	for (u32 i = 0; i < skb_n; i++) {
+		struct sk_buff *skb = skbs[i];
+
 		act = bpf_prog_run_generic_xdp(skb, &xdp, rcpu->prog);
 		switch (act) {
 		case XDP_PASS:
+			napi_gro_receive(&rcpu->napi, skb);
+			stats->pass++;
 			break;
 		case XDP_REDIRECT:
-			skb_list_del_init(skb);
 			err = xdp_do_generic_redirect(skb->dev, skb, &xdp,
 						      rcpu->prog);
 			if (unlikely(err)) {
@@ -181,8 +183,7 @@ static void cpu_map_bpf_prog_run_skb(struct bpf_cpu_map_entry *rcpu,
 			trace_xdp_exception(skb->dev, rcpu->prog, act);
 			fallthrough;
 		case XDP_DROP:
-			skb_list_del_init(skb);
-			kfree_skb(skb);
+			napi_consume_skb(skb, true);
 			stats->drop++;
 			return;
 		}
@@ -251,8 +252,8 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
 #define CPUMAP_BATCH 8
 
 static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
-				int xdp_n, struct xdp_cpumap_stats *stats,
-				struct list_head *list)
+				int xdp_n, void **skbs, u32 skb_n,
+				struct xdp_cpumap_stats *stats)
 {
 	struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
 	int nframes;
@@ -267,8 +268,8 @@ static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
 	if (stats->redirect)
 		xdp_do_flush();
 
-	if (unlikely(!list_empty(list)))
-		cpu_map_bpf_prog_run_skb(rcpu, list, stats);
+	if (unlikely(skb_n))
+		cpu_map_bpf_prog_run_skb(rcpu, skbs, skb_n, stats);
 
 	bpf_net_ctx_clear(bpf_net_ctx);
 
@@ -288,9 +289,7 @@ static int cpu_map_napi_poll(struct napi_struct *napi, int budget)
 		gfp_t gfp = __GFP_ZERO | GFP_ATOMIC;
 		int i, n, m, nframes, xdp_n;
 		void *frames[CPUMAP_BATCH];
-		struct sk_buff *skb, *tmp;
 		void *skbs[CPUMAP_BATCH];
-		LIST_HEAD(list);
 
 		if (__ptr_ring_empty(rcpu->queue))
 			break;
@@ -304,15 +303,15 @@ static int cpu_map_napi_poll(struct napi_struct *napi, int budget)
 		n = __ptr_ring_consume_batched(rcpu->queue, frames, n);
 		done += n;
 
-		for (i = 0, xdp_n = 0; i < n; i++) {
+		for (i = 0, xdp_n = 0, m = 0; i < n; i++) {
 			void *f = frames[i];
 			struct page *page;
 
 			if (unlikely(__ptr_test_bit(0, &f))) {
-				skb = f;
+				struct sk_buff *skb = f;
 
 				__ptr_clear_bit(0, &skb);
-				list_add_tail(&skb->list, &list);
+				skbs[m++] = skb;
 				continue;
 			}
 
@@ -327,19 +326,22 @@ static int cpu_map_napi_poll(struct napi_struct *napi, int budget)
 		}
 
 		/* Support running another XDP prog on this CPU */
-		nframes = cpu_map_bpf_prog_run(rcpu, frames, xdp_n, &stats, &list);
-		if (nframes) {
-			m = kmem_cache_alloc_bulk(net_hotdata.skbuff_cache,
-						  gfp, nframes, skbs);
-			if (unlikely(m == 0)) {
-				for (i = 0; i < nframes; i++)
-					skbs[i] = NULL; /* effect: xdp_return_frame */
-				kmem_alloc_drops += nframes;
-			}
+		nframes = cpu_map_bpf_prog_run(rcpu, frames, xdp_n, skbs, m,
+					       &stats);
+		if (!nframes)
+			continue;
+
+		m = kmem_cache_alloc_bulk(net_hotdata.skbuff_cache, gfp,
+					  nframes, skbs);
+		if (unlikely(!m)) {
+			for (i = 0; i < nframes; i++)
+				skbs[i] = NULL; /* effect: xdp_return_frame */
+			kmem_alloc_drops += nframes;
 		}
 
 		for (i = 0; i < nframes; i++) {
 			struct xdp_frame *xdpf = frames[i];
+			struct sk_buff *skb;
 
 			skb = __xdp_build_skb_from_frame(xdpf, skbs[i],
 							 xdpf->dev_rx);
@@ -348,11 +350,6 @@ static int cpu_map_napi_poll(struct napi_struct *napi, int budget)
 				continue;
 			}
 
-			list_add_tail(&skb->list, &list);
-		}
-
-		list_for_each_entry_safe(skb, tmp, &list, list) {
-			skb_list_del_init(skb);
 			napi_gro_receive(napi, skb);
 		}
 	}
-- 
2.46.0