cfg80211: reuse existing page fragments in A-MSDU rx

This massively reduces data copying and thus improves rx performance

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 77 insertions, 5 deletions

diff --git a/net/wireless/util.c b/net/wireless/util.c
index 9880c894c58d..c7f6820bb258 100644
--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -644,23 +644,93 @@ int ieee80211_data_from_8023(struct sk_buff *skb, const u8 *addr,
 }
 EXPORT_SYMBOL(ieee80211_data_from_8023);
 
+static void
+__frame_add_frag(struct sk_buff *skb, struct page *page,
+                 void *ptr, int len, int size)
+{
+        struct skb_shared_info *sh = skb_shinfo(skb);
+        int page_offset;
+
+        atomic_inc(&page->_count);
+        page_offset = ptr - page_address(page);
+        skb_add_rx_frag(skb, sh->nr_frags, page, page_offset, len, size);
+}
+
+static void
+__ieee80211_amsdu_copy_frag(struct sk_buff *skb, struct sk_buff *frame,
+                            int offset, int len)
+{
+        struct skb_shared_info *sh = skb_shinfo(skb);
+        const skb_frag_t *frag = &sh->frags[-1];
+        struct page *frag_page;
+        void *frag_ptr;
+        int frag_len, frag_size;
+        int head_size = skb->len - skb->data_len;
+        int cur_len;
+
+        frag_page = virt_to_head_page(skb->head);
+        frag_ptr = skb->data;
+        frag_size = head_size;
+
+        while (offset >= frag_size) {
+                offset -= frag_size;
+                frag++;
+                frag_page = skb_frag_page(frag);
+                frag_ptr = skb_frag_address(frag);
+                frag_size = skb_frag_size(frag);
+        }
+
+        frag_ptr += offset;
+        frag_len = frag_size - offset;
+
+        cur_len = min(len, frag_len);
+
+        __frame_add_frag(frame, frag_page, frag_ptr, cur_len, frag_size);
+        len -= cur_len;
+
+        while (len > 0) {
+                frag++;
+                frag_len = skb_frag_size(frag);
+                cur_len = min(len, frag_len);
+                __frame_add_frag(frame, skb_frag_page(frag),
+                                 skb_frag_address(frag), cur_len, frag_len);
+                len -= cur_len;
+        }
+}
+
 static struct sk_buff *
 __ieee80211_amsdu_copy(struct sk_buff *skb, unsigned int hlen,
-                       int offset, int len)
+                       int offset, int len, bool reuse_frag)
 {
         struct sk_buff *frame;
+        int cur_len = len;
 
         if (skb->len - offset < len)
                 return NULL;
 
         /*
+         * When reusing framents, copy some data to the head to simplify
+         * ethernet header handling and speed up protocol header processing
+         * in the stack later.
+         */
+        if (reuse_frag)
+                cur_len = min_t(int, len, 32);
+
+        /*
          * Allocate and reserve two bytes more for payload
          * alignment since sizeof(struct ethhdr) is 14.
          */
-        frame = dev_alloc_skb(hlen + sizeof(struct ethhdr) + 2 + len);
+        frame = dev_alloc_skb(hlen + sizeof(struct ethhdr) + 2 + cur_len);
 
         skb_reserve(frame, hlen + sizeof(struct ethhdr) + 2);
-        skb_copy_bits(skb, offset, skb_put(frame, len), len);
+        skb_copy_bits(skb, offset, skb_put(frame, cur_len), cur_len);
+
+        len -= cur_len;
+        if (!len)
+                return frame;
+
+        offset += cur_len;
+        __ieee80211_amsdu_copy_frag(skb, frame, offset, len);
 
         return frame;
 }
@@ -676,6 +746,7 @@ void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list,
         u8 *payload;
         int offset = 0, remaining, err;
         struct ethhdr eth;
+        bool reuse_frag = skb->head_frag && !skb_has_frag_list(skb);
         bool reuse_skb = false;
         bool last = false;
 
@@ -703,12 +774,13 @@ void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list,
                 offset += sizeof(struct ethhdr);
                 /* reuse skb for the last subframe */
                 last = remaining <= subframe_len + padding;
-                if (!skb_is_nonlinear(skb) && last) {
+                if (!skb_is_nonlinear(skb) && !reuse_frag && last) {
                         skb_pull(skb, offset);
                         frame = skb;
                         reuse_skb = true;
                 } else {
-                        frame = __ieee80211_amsdu_copy(skb, hlen, offset, len);
+                        frame = __ieee80211_amsdu_copy(skb, hlen, offset, len,
+                                                       reuse_frag);
                         if (!frame)
                                 goto purge;