mac80211: add TX fastpath

In order to speed up mac80211's TX path, add the "fast-xmit" cache
that will cache the data frame 802.11 header and other data to be
able to build the frame more quickly. This cache is rebuilt when
external triggers imply changes, but a lot of the checks done per
packet today are simplified away to the check for the cache.

There's also a more detailed description in the code.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 419 insertions, 1 deletions

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 667111e..160e1927 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1600,7 +1600,7 @@ static int ieee80211_skb_resize(struct ieee80211_sub_if_data *sdata,
 	if (skb_cloned(skb) &&
 	    (!(local->hw.flags & IEEE80211_HW_SUPPORTS_CLONED_SKBS) ||
 	     !skb_clone_writable(skb, ETH_HLEN) ||
-	     sdata->crypto_tx_tailroom_needed_cnt))
+	     (may_encrypt && sdata->crypto_tx_tailroom_needed_cnt)))
 		I802_DEBUG_INC(local->tx_expand_skb_head_cloned);
 	else if (head_need || tail_need)
 		I802_DEBUG_INC(local->tx_expand_skb_head);
@@ -2387,6 +2387,414 @@ static struct sk_buff *ieee80211_build_hdr(struct ieee80211_sub_if_data *sdata,
 	return ERR_PTR(ret);
 }
 
+/*
+ * fast-xmit overview
+ *
+ * The core idea of this fast-xmit is to remove per-packet checks by checking
+ * them out of band. ieee80211_check_fast_xmit() implements the out-of-band
+ * checks that are needed to get the sta->fast_tx pointer assigned, after which
+ * much less work can be done per packet. For example, fragmentation must be
+ * disabled or the fast_tx pointer will not be set. All the conditions are seen
+ * in the code here.
+ *
+ * Once assigned, the fast_tx data structure also caches the per-packet 802.11
+ * header and other data to aid packet processing in ieee80211_xmit_fast().
+ *
+ * The most difficult part of this is that when any of these assumptions
+ * change, an external trigger (i.e. a call to ieee80211_clear_fast_xmit(),
+ * ieee80211_check_fast_xmit() or friends) is required to reset the data,
+ * since the per-packet code no longer checks the conditions. This is reflected
+ * by the calls to these functions throughout the rest of the code, and must be
+ * maintained if any of the TX path checks change.
+ */
+
+void ieee80211_check_fast_xmit(struct sta_info *sta)
+{
+	struct ieee80211_fast_tx build = {}, *fast_tx = NULL, *old;
+	struct ieee80211_local *local = sta->local;
+	struct ieee80211_sub_if_data *sdata = sta->sdata;
+	struct ieee80211_hdr *hdr = (void *)build.hdr;
+	struct ieee80211_chanctx_conf *chanctx_conf;
+	__le16 fc;
+
+	if (!(local->hw.flags & IEEE80211_HW_SUPPORT_FAST_XMIT))
+		return;
+
+	/* Locking here protects both the pointer itself, and against concurrent
+	 * invocations winning data access races to, e.g., the key pointer that
+	 * is used.
+	 * Without it, the invocation of this function right after the key
+	 * pointer changes wouldn't be sufficient, as another CPU could access
+	 * the pointer, then stall, and then do the cache update after the CPU
+	 * that invalidated the key.
+	 * With the locking, such scenarios cannot happen as the check for the
+	 * key and the fast-tx assignment are done atomically, so the CPU that
+	 * modifies the key will either wait or other one will see the key
+	 * cleared/changed already.
+	 */
+	spin_lock_bh(&sta->lock);
+	if (local->hw.flags & IEEE80211_HW_SUPPORTS_PS &&
+	    !(local->hw.flags & IEEE80211_HW_SUPPORTS_DYNAMIC_PS) &&
+	    sdata->vif.type == NL80211_IFTYPE_STATION)
+		goto out;
+
+	if (!test_sta_flag(sta, WLAN_STA_AUTHORIZED))
+		goto out;
+
+	if (test_sta_flag(sta, WLAN_STA_PS_STA) ||
+	    test_sta_flag(sta, WLAN_STA_PS_DRIVER) ||
+	    test_sta_flag(sta, WLAN_STA_PS_DELIVER))
+		goto out;
+
+	if (sdata->noack_map)
+		goto out;
+
+	/* fast-xmit doesn't handle fragmentation at all */
+	if (local->hw.wiphy->frag_threshold != (u32)-1)
+		goto out;
+
+	rcu_read_lock();
+	chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf);
+	if (!chanctx_conf) {
+		rcu_read_unlock();
+		goto out;
+	}
+	build.band = chanctx_conf->def.chan->band;
+	rcu_read_unlock();
+
+	fc = cpu_to_le16(IEEE80211_FTYPE_DATA | IEEE80211_STYPE_DATA);
+
+	switch (sdata->vif.type) {
+	case NL80211_IFTYPE_STATION:
+		if (test_sta_flag(sta, WLAN_STA_TDLS_PEER)) {
+			/* DA SA BSSID */
+			build.da_offs = offsetof(struct ieee80211_hdr, addr1);
+			build.sa_offs = offsetof(struct ieee80211_hdr, addr2);
+			memcpy(hdr->addr3, sdata->u.mgd.bssid, ETH_ALEN);
+			build.hdr_len = 24;
+			break;
+		}
+
+		if (sdata->u.mgd.use_4addr) {
+			/* non-regular ethertype cannot use the fastpath */
+			fc |= cpu_to_le16(IEEE80211_FCTL_FROMDS |
+					  IEEE80211_FCTL_TODS);
+			/* RA TA DA SA */
+			memcpy(hdr->addr1, sdata->u.mgd.bssid, ETH_ALEN);
+			memcpy(hdr->addr2, sdata->vif.addr, ETH_ALEN);
+			build.da_offs = offsetof(struct ieee80211_hdr, addr3);
+			build.sa_offs = offsetof(struct ieee80211_hdr, addr4);
+			build.hdr_len = 30;
+			break;
+		}
+		fc |= cpu_to_le16(IEEE80211_FCTL_TODS);
+		/* BSSID SA DA */
+		memcpy(hdr->addr1, sdata->u.mgd.bssid, ETH_ALEN);
+		build.da_offs = offsetof(struct ieee80211_hdr, addr3);
+		build.sa_offs = offsetof(struct ieee80211_hdr, addr2);
+		build.hdr_len = 24;
+		break;
+	case NL80211_IFTYPE_AP_VLAN:
+		if (sdata->wdev.use_4addr) {
+			fc |= cpu_to_le16(IEEE80211_FCTL_FROMDS |
+					  IEEE80211_FCTL_TODS);
+			/* RA TA DA SA */
+			memcpy(hdr->addr1, sta->sta.addr, ETH_ALEN);
+			memcpy(hdr->addr2, sdata->vif.addr, ETH_ALEN);
+			build.da_offs = offsetof(struct ieee80211_hdr, addr3);
+			build.sa_offs = offsetof(struct ieee80211_hdr, addr4);
+			build.hdr_len = 30;
+			break;
+		}
+		/* fall through */
+	case NL80211_IFTYPE_AP:
+		fc |= cpu_to_le16(IEEE80211_FCTL_FROMDS);
+		/* DA BSSID SA */
+		build.da_offs = offsetof(struct ieee80211_hdr, addr1);
+		memcpy(hdr->addr2, sdata->vif.addr, ETH_ALEN);
+		build.sa_offs = offsetof(struct ieee80211_hdr, addr3);
+		build.hdr_len = 24;
+		break;
+	default:
+		/* not handled on fast-xmit */
+		goto out;
+	}
+
+	if (sta->sta.wme) {
+		build.hdr_len += 2;
+		fc |= cpu_to_le16(IEEE80211_STYPE_QOS_DATA);
+	}
+
+	/* We store the key here so there's no point in using rcu_dereference()
+	 * but that's fine because the code that changes the pointers will call
+	 * this function after doing so. For a single CPU that would be enough,
+	 * for multiple see the comment above.
+	 */
+	build.key = rcu_access_pointer(sta->ptk[sta->ptk_idx]);
+	if (!build.key)
+		build.key = rcu_access_pointer(sdata->default_unicast_key);
+	if (build.key) {
+		bool gen_iv, iv_spc;
+
+		gen_iv = build.key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_IV;
+		iv_spc = build.key->conf.flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE;
+
+		/* don't handle software crypto */
+		if (!(build.key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE))
+			goto out;
+
+		switch (build.key->conf.cipher) {
+		case WLAN_CIPHER_SUITE_CCMP:
+		case WLAN_CIPHER_SUITE_CCMP_256:
+			/* add fixed key ID */
+			if (gen_iv) {
+				(build.hdr + build.hdr_len)[3] =
+					0x20 | (build.key->conf.keyidx << 6);
+				build.pn_offs = build.hdr_len;
+			}
+			if (gen_iv || iv_spc)
+				build.hdr_len += IEEE80211_CCMP_HDR_LEN;
+			break;
+		case WLAN_CIPHER_SUITE_GCMP:
+		case WLAN_CIPHER_SUITE_GCMP_256:
+			/* add fixed key ID */
+			if (gen_iv) {
+				(build.hdr + build.hdr_len)[3] =
+					0x20 | (build.key->conf.keyidx << 6);
+				build.pn_offs = build.hdr_len;
+			}
+			if (gen_iv || iv_spc)
+				build.hdr_len += IEEE80211_GCMP_HDR_LEN;
+			break;
+		default:
+			/* don't do fast-xmit for these ciphers (yet) */
+			goto out;
+		}
+
+		fc |= cpu_to_le16(IEEE80211_FCTL_PROTECTED);
+	}
+
+	hdr->frame_control = fc;
+
+	memcpy(build.hdr + build.hdr_len,
+	       rfc1042_header,  sizeof(rfc1042_header));
+	build.hdr_len += sizeof(rfc1042_header);
+
+	fast_tx = kmemdup(&build, sizeof(build), GFP_ATOMIC);
+	/* if the kmemdup fails, continue w/o fast_tx */
+	if (!fast_tx)
+		goto out;
+
+ out:
+	/* we might have raced against another call to this function */
+	old = rcu_dereference_protected(sta->fast_tx,
+					lockdep_is_held(&sta->lock));
+	rcu_assign_pointer(sta->fast_tx, fast_tx);
+	if (old)
+		kfree_rcu(old, rcu_head);
+	spin_unlock_bh(&sta->lock);
+}
+
+void ieee80211_check_fast_xmit_all(struct ieee80211_local *local)
+{
+	struct sta_info *sta;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(sta, &local->sta_list, list)
+		ieee80211_check_fast_xmit(sta);
+	rcu_read_unlock();
+}
+
+void ieee80211_check_fast_xmit_iface(struct ieee80211_sub_if_data *sdata)
+{
+	struct ieee80211_local *local = sdata->local;
+	struct sta_info *sta;
+
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(sta, &local->sta_list, list) {
+		if (sdata != sta->sdata &&
+		    (!sta->sdata->bss || sta->sdata->bss != sdata->bss))
+			continue;
+		ieee80211_check_fast_xmit(sta);
+	}
+
+	rcu_read_unlock();
+}
+
+void ieee80211_clear_fast_xmit(struct sta_info *sta)
+{
+	struct ieee80211_fast_tx *fast_tx;
+
+	spin_lock_bh(&sta->lock);
+	fast_tx = rcu_dereference_protected(sta->fast_tx,
+					    lockdep_is_held(&sta->lock));
+	RCU_INIT_POINTER(sta->fast_tx, NULL);
+	spin_unlock_bh(&sta->lock);
+
+	if (fast_tx)
+		kfree_rcu(fast_tx, rcu_head);
+}
+
+static bool ieee80211_xmit_fast(struct ieee80211_sub_if_data *sdata,
+				struct net_device *dev, struct sta_info *sta,
+				struct ieee80211_fast_tx *fast_tx,
+				struct sk_buff *skb)
+{
+	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 = IEEE80211_SKB_CB(skb);
+	struct ieee80211_hdr *hdr = (void *)fast_tx->hdr;
+	struct ieee80211_tx_data tx;
+	ieee80211_tx_result r;
+	struct tid_ampdu_tx *tid_tx = NULL;
+	u8 tid = IEEE80211_NUM_TIDS;
+
+	/* control port protocol needs a lot of special handling */
+	if (cpu_to_be16(ethertype) == sdata->control_port_protocol)
+		return false;
+
+	/* only RFC 1042 SNAP */
+	if (ethertype < ETH_P_802_3_MIN)
+		return false;
+
+	/* don't handle TX status request here either */
+	if (skb->sk && skb_shinfo(skb)->tx_flags & SKBTX_WIFI_STATUS)
+		return false;
+
+	if (hdr->frame_control & cpu_to_le16(IEEE80211_STYPE_QOS_DATA)) {
+		tid = skb->priority & IEEE80211_QOS_CTL_TAG1D_MASK;
+		tid_tx = rcu_dereference(sta->ampdu_mlme.tid_tx[tid]);
+		if (tid_tx &&
+		    !test_bit(HT_AGG_STATE_OPERATIONAL, &tid_tx->state))
+			return false;
+	}
+
+	/* after this point (skb is modified) we cannot return false */
+
+	if (skb_shared(skb)) {
+		struct sk_buff *tmp_skb = skb;
+
+		skb = skb_clone(skb, GFP_ATOMIC);
+		kfree_skb(tmp_skb);
+
+		if (!skb)
+			return true;
+	}
+
+	dev->stats.tx_packets++;
+	dev->stats.tx_bytes += skb->len + extra_head;
+	dev->trans_start = jiffies;
+
+	/* will not be crypto-handled beyond what we do here, so use false
+	 * 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))) {
+		kfree_skb(skb);
+		return true;
+	}
+
+	memcpy(&eth, skb->data, ETH_HLEN - 2);
+	hdr = (void *)skb_push(skb, extra_head);
+	memcpy(skb->data, fast_tx->hdr, fast_tx->hdr_len);
+	memcpy(skb->data + fast_tx->da_offs, eth.h_dest, ETH_ALEN);
+	memcpy(skb->data + fast_tx->sa_offs, eth.h_source, ETH_ALEN);
+
+	memset(info, 0, sizeof(*info));
+	info->band = fast_tx->band;
+	info->control.vif = &sdata->vif;
+	info->flags = IEEE80211_TX_CTL_FIRST_FRAGMENT |
+		      IEEE80211_TX_CTL_DONTFRAG |
+		      (tid_tx ? IEEE80211_TX_CTL_AMPDU : 0);
+
+	if (hdr->frame_control & cpu_to_le16(IEEE80211_STYPE_QOS_DATA)) {
+		*ieee80211_get_qos_ctl(hdr) = tid;
+		hdr->seq_ctrl = ieee80211_tx_next_seq(sta, tid);
+	} else {
+		info->flags |= IEEE80211_TX_CTL_ASSIGN_SEQ;
+		hdr->seq_ctrl = cpu_to_le16(sdata->sequence_number);
+		sdata->sequence_number += 0x10;
+	}
+
+	sta->tx_msdu[tid]++;
+
+	info->hw_queue = sdata->vif.hw_queue[skb_get_queue_mapping(skb)];
+
+	__skb_queue_head_init(&tx.skbs);
+
+	tx.flags = IEEE80211_TX_UNICAST;
+	tx.local = local;
+	tx.sdata = sdata;
+	tx.sta = sta;
+	tx.key = fast_tx->key;
+
+	if (fast_tx->key)
+		info->control.hw_key = &fast_tx->key->conf;
+
+	if (!(local->hw.flags & IEEE80211_HW_HAS_RATE_CONTROL)) {
+		tx.skb = skb;
+		r = ieee80211_tx_h_rate_ctrl(&tx);
+		skb = tx.skb;
+		tx.skb = NULL;
+
+		if (r != TX_CONTINUE) {
+			if (r != TX_QUEUED)
+				kfree_skb(skb);
+			return true;
+		}
+	}
+
+	/* statistics normally done by ieee80211_tx_h_stats (but that
+	 * has to consider fragmentation, so is more complex)
+	 */
+	sta->tx_fragments++;
+	sta->tx_bytes[skb_get_queue_mapping(skb)] += skb->len;
+	sta->tx_packets[skb_get_queue_mapping(skb)]++;
+
+	if (fast_tx->pn_offs) {
+		u64 pn;
+		u8 *crypto_hdr = skb->data + fast_tx->pn_offs;
+
+		switch (fast_tx->key->conf.cipher) {
+		case WLAN_CIPHER_SUITE_CCMP:
+		case WLAN_CIPHER_SUITE_CCMP_256:
+			pn = atomic64_inc_return(&fast_tx->key->u.ccmp.tx_pn);
+			crypto_hdr[0] = pn;
+			crypto_hdr[1] = pn >> 8;
+			crypto_hdr[4] = pn >> 16;
+			crypto_hdr[5] = pn >> 24;
+			crypto_hdr[6] = pn >> 32;
+			crypto_hdr[7] = pn >> 40;
+			break;
+		case WLAN_CIPHER_SUITE_GCMP:
+		case WLAN_CIPHER_SUITE_GCMP_256:
+			pn = atomic64_inc_return(&fast_tx->key->u.gcmp.tx_pn);
+			crypto_hdr[0] = pn;
+			crypto_hdr[1] = pn >> 8;
+			crypto_hdr[4] = pn >> 16;
+			crypto_hdr[5] = pn >> 24;
+			crypto_hdr[6] = pn >> 32;
+			crypto_hdr[7] = pn >> 40;
+			break;
+		}
+	}
+
+	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
+		sdata = container_of(sdata->bss,
+				     struct ieee80211_sub_if_data, u.ap);
+
+	__skb_queue_tail(&tx.skbs, skb);
+	ieee80211_tx_frags(local, &sdata->vif, &sta->sta, &tx.skbs, false);
+	return true;
+}
+
 void __ieee80211_subif_start_xmit(struct sk_buff *skb,
 				  struct net_device *dev,
 				  u32 info_flags)
@@ -2406,6 +2814,16 @@ void __ieee80211_subif_start_xmit(struct sk_buff *skb,
 		goto out;
 	}
 
+	if (!IS_ERR_OR_NULL(sta)) {
+		struct ieee80211_fast_tx *fast_tx;
+
+		fast_tx = rcu_dereference(sta->fast_tx);
+
+		if (fast_tx &&
+		    ieee80211_xmit_fast(sdata, dev, sta, fast_tx, skb))
+			goto out;
+	}
+
 	skb = ieee80211_build_hdr(sdata, skb, info_flags, sta);
 	if (IS_ERR(skb))
 		goto out;