mac80211: optimize skb resizing to avoid reallocation when using 802.11s + batman-adv

Signed-off-by: Felix Fietkau <[email protected]>

package/kernel/mac80211/patches/subsys/357-mac80211-optimize-skb-resizing.patch

@@ -0,0 +1,198 @@
+From: Felix Fietkau <[email protected]>
+Date: Sun, 17 Mar 2019 18:11:30 +0100
+Subject: [PATCH] mac80211: optimize skb resizing
+
+When forwarding unicast packets from ethernet to batman-adv over 802.11s
+(with forwarding disabled), the typical required headroom to transmit
+encrypted packets on mt76 is 32 (802.11) + 6 (802.11s) + 8 (CCMP) +
+2 (padding) + 6 (LLC) + 18 (batman-adv) - 14 (old ethernet header) = 58 bytes.
+
+On systems where NET_SKB_PAD is 64 this leads to a call to pskb_expand_head
+for every packet, since mac80211 also tries to allocate 16 bytes status
+headroom for radiotap headers.
+
+This patch fixes these unnecessary reallocations by only requiring the extra
+status headroom in ieee80211_tx_monitor()
+If however a reallocation happens before that call, the status headroom gets
+added there as well, in order to avoid double reallocation.
+
+The patch also cleans up the code by moving the headroom calculation to
+ieee80211_skb_resize.
+
+Signed-off-by: Felix Fietkau <[email protected]>
+---
+
+--- a/net/mac80211/ieee80211_i.h
++++ b/net/mac80211/ieee80211_i.h
+@@ -1761,6 +1761,8 @@ void ieee80211_clear_fast_xmit(struct st
+ int ieee80211_tx_control_port(struct wiphy *wiphy, struct net_device *dev,
+ 			      const u8 *buf, size_t len,
+ 			      const u8 *dest, __be16 proto, bool unencrypted);
++int ieee80211_skb_resize(struct ieee80211_sub_if_data *sdata,
++			 struct sk_buff *skb, int hdrlen, int hdr_add);
+ 
+ /* HT */
+ void ieee80211_apply_htcap_overrides(struct ieee80211_sub_if_data *sdata,
+--- a/net/mac80211/status.c
++++ b/net/mac80211/status.c
+@@ -672,6 +672,11 @@ void ieee80211_tx_monitor(struct ieee802
+ 		}
+ 	}
+ 
++	if (ieee80211_skb_resize(NULL, skb, 0, 0)) {
++		dev_kfree_skb(skb);
++		return;
++	}
++
+ 	/* send frame to monitor interfaces now */
+ 	rtap_len = ieee80211_tx_radiotap_len(info);
+ 	if (WARN_ON_ONCE(skb_headroom(skb) < rtap_len)) {
+--- a/net/mac80211/tx.c
++++ b/net/mac80211/tx.c
+@@ -1914,37 +1914,53 @@ static bool ieee80211_tx(struct ieee8021
+ }
+ 
+ /* device xmit handlers */
+-
+-static int ieee80211_skb_resize(struct ieee80211_sub_if_data *sdata,
+-				struct sk_buff *skb,
+-				int head_need, bool may_encrypt)
++int ieee80211_skb_resize(struct ieee80211_sub_if_data *sdata,
++			 struct sk_buff *skb, int hdr_len, int hdr_extra)
+ {
+ 	struct ieee80211_local *local = sdata->local;
++	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+ 	struct ieee80211_hdr *hdr;
+-	bool enc_tailroom;
+-	int tail_need = 0;
++	int head_need, head_max;
++	int tail_need, tail_max;
++	bool enc_tailroom = false;
+ 
+-	hdr = (struct ieee80211_hdr *) skb->data;
+-	enc_tailroom = may_encrypt &&
+-		       (sdata->crypto_tx_tailroom_needed_cnt ||
+-			ieee80211_is_mgmt(hdr->frame_control));
++	if (sdata && !hdr_len &&
++	    !(info->flags & IEEE80211_TX_INTFL_DONT_ENCRYPT)) {
++		hdr = (struct ieee80211_hdr *) skb->data;
++		enc_tailroom = (sdata->crypto_tx_tailroom_needed_cnt ||
++				ieee80211_is_mgmt(hdr->frame_control));
++		hdr_len += sdata->encrypt_headroom;
++	}
+ 
+-	if (enc_tailroom) {
+-		tail_need = IEEE80211_ENCRYPT_TAILROOM;
+-		tail_need -= skb_tailroom(skb);
+-		tail_need = max_t(int, tail_need, 0);
++	head_need = head_max = hdr_len;
++	tail_need = tail_max = 0;
++	if (!sdata) {
++		head_need = head_max = local->tx_headroom;
++	} else {
++		head_max += hdr_extra;
++		head_max += max_t(int, local->tx_headroom,
++				  local->hw.extra_tx_headroom);
++		head_need += local->hw.extra_tx_headroom;
++
++		tail_max = IEEE80211_ENCRYPT_TAILROOM;
++		if (enc_tailroom)
++			tail_need = tail_max;
+ 	}
+ 
+ 	if (skb_cloned(skb) &&
+ 	    (!ieee80211_hw_check(&local->hw, SUPPORTS_CLONED_SKBS) ||
+ 	     !skb_clone_writable(skb, ETH_HLEN) || enc_tailroom))
+ 		I802_DEBUG_INC(local->tx_expand_skb_head_cloned);
+-	else if (head_need || tail_need)
++	else if (head_need > skb_headroom(skb) ||
++		 tail_need > skb_tailroom(skb))
+ 		I802_DEBUG_INC(local->tx_expand_skb_head);
+ 	else
+ 		return 0;
+ 
+-	if (pskb_expand_head(skb, head_need, tail_need, GFP_ATOMIC)) {
++	head_max = max_t(int, 0, head_max - skb_headroom(skb));
++	tail_max = max_t(int, 0, tail_max - skb_tailroom(skb));
++
++	if (pskb_expand_head(skb, head_max, tail_max, GFP_ATOMIC)) {
+ 		wiphy_debug(local->hw.wiphy,
+ 			    "failed to reallocate TX buffer\n");
+ 		return -ENOMEM;
+@@ -1960,18 +1976,8 @@ void ieee80211_xmit(struct ieee80211_sub
+ 	struct ieee80211_local *local = sdata->local;
+ 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+ 	struct ieee80211_hdr *hdr;
+-	int headroom;
+-	bool may_encrypt;
+-
+-	may_encrypt = !(info->flags & IEEE80211_TX_INTFL_DONT_ENCRYPT);
+-
+-	headroom = local->tx_headroom;
+-	if (may_encrypt)
+-		headroom += sdata->encrypt_headroom;
+-	headroom -= skb_headroom(skb);
+-	headroom = max_t(int, 0, headroom);
+ 
+-	if (ieee80211_skb_resize(sdata, skb, headroom, may_encrypt)) {
++	if (ieee80211_skb_resize(sdata, skb, 0, 0)) {
+ 		ieee80211_free_txskb(&local->hw, skb);
+ 		return;
+ 	}
+@@ -2740,30 +2746,14 @@ static struct sk_buff *ieee80211_build_h
+ 
+ 	skb_pull(skb, skip_header_bytes);
+ 	padsize = ieee80211_hdr_padsize(&local->hw, hdrlen);
+-	head_need = hdrlen + encaps_len + meshhdrlen - skb_headroom(skb);
++	head_need = hdrlen + encaps_len + meshhdrlen;
+ 	head_need += padsize;
+ 
+-	/*
+-	 * So we need to modify the skb header and hence need a copy of
+-	 * that. The head_need variable above doesn't, so far, include
+-	 * the needed header space that we don't need right away. If we
+-	 * can, then we don't reallocate right now but only after the
+-	 * frame arrives at the master device (if it does...)
+-	 *
+-	 * If we cannot, however, then we will reallocate to include all
+-	 * the ever needed space. Also, if we need to reallocate it anyway,
+-	 * make it big enough for everything we may ever need.
+-	 */
+-
+-	if (head_need > 0 || skb_cloned(skb)) {
+-		head_need += sdata->encrypt_headroom;
+-		head_need += local->tx_headroom;
+-		head_need = max_t(int, 0, head_need);
+-		if (ieee80211_skb_resize(sdata, skb, head_need, true)) {
+-			ieee80211_free_txskb(&local->hw, skb);
+-			skb = NULL;
+-			return ERR_PTR(-ENOMEM);
+-		}
++	if (ieee80211_skb_resize(sdata, skb, head_need,
++				 sdata->encrypt_headroom)) {
++		ieee80211_free_txskb(&local->hw, skb);
++		skb = NULL;
++		return ERR_PTR(-ENOMEM);
+ 	}
+ 
+ 	if (encaps_data)
+@@ -3377,7 +3367,6 @@ static bool ieee80211_xmit_fast(struct i
+ 	struct ieee80211_local *local = sdata->local;
+ 	u16 ethertype = (skb->data[12] << 8) | skb->data[13];
+ 	int extra_head = fast_tx->hdr_len - (ETH_HLEN - 2);
+-	int hw_headroom = sdata->local->hw.extra_tx_headroom;
+ 	struct ethhdr eth;
+ 	struct ieee80211_tx_info *info;
+ 	struct ieee80211_hdr *hdr = (void *)fast_tx->hdr;
+@@ -3429,10 +3418,7 @@ static bool ieee80211_xmit_fast(struct i
+ 	 * as the may-encrypt argument for the resize to not account for
+ 	 * more room than we already have in 'extra_head'
+ 	 */
+-	if (unlikely(ieee80211_skb_resize(sdata, skb,
+-					  max_t(int, extra_head + hw_headroom -
+-						     skb_headroom(skb), 0),
+-					  false))) {
++	if (unlikely(ieee80211_skb_resize(sdata, skb, extra_head, 0))) {
+ 		kfree_skb(skb);
+ 		return true;
+ 	}