carl9170: revamp carl9170_tx_prepare

David Miller complained about the driver's excessive use
of variables in __packed structs. While I did not fully
agree with his sole "performance" argument on all accounts.
I do see some room for improvement in hot-paths on
architectures without an efficient access to unaligned
elements.

This first patch (dare I say?) optimizes an important tx
hot-path in the driver: carl9170_tx_prepare.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 75 insertions, 80 deletions

diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c
index e6be5e6c1723..b575c865142d 100644
--- a/drivers/net/wireless/ath/carl9170/tx.c
+++ b/drivers/net/wireless/ath/carl9170/tx.c
@@ -760,8 +760,8 @@ static int carl9170_tx_prepare(struct ar9170 *ar, struct sk_buff *skb)
         struct carl9170_tx_info *arinfo;
         unsigned int hw_queue;
         int i;
-        u16 keytype = 0;
-        u16 len, icv = 0;
+        __le16 mac_tmp;
+        u16 len;
         bool ampdu, no_ack;
 
         BUILD_BUG_ON(sizeof(*arinfo) > sizeof(info->rate_driver_data));
@@ -773,6 +773,10 @@ static int carl9170_tx_prepare(struct ar9170 *ar, struct sk_buff *skb)
 
         BUILD_BUG_ON(IEEE80211_TX_MAX_RATES < CARL9170_TX_MAX_RATES);
 
+        BUILD_BUG_ON(AR9170_MAX_VIRTUAL_MAC >
+                ((CARL9170_TX_SUPER_MISC_VIF_ID >>
+                 CARL9170_TX_SUPER_MISC_VIF_ID_S) + 1));
+
         hw_queue = ar9170_qmap[carl9170_get_queue(ar, skb)];
 
         hdr = (void *)skb->data;
@@ -793,20 +797,37 @@ static int carl9170_tx_prepare(struct ar9170 *ar, struct sk_buff *skb)
         txc = (void *)skb_push(skb, sizeof(*txc));
         memset(txc, 0, sizeof(*txc));
 
-        ampdu = !!(info->flags & IEEE80211_TX_CTL_AMPDU);
+        SET_VAL(CARL9170_TX_SUPER_MISC_QUEUE, txc->s.misc, hw_queue);
+
+        if (likely(cvif))
+                SET_VAL(CARL9170_TX_SUPER_MISC_VIF_ID, txc->s.misc, cvif->id);
+
+        if (unlikely(info->flags & IEEE80211_TX_CTL_SEND_AFTER_DTIM))
+                txc->s.misc |= CARL9170_TX_SUPER_MISC_CAB;
+
+        if (unlikely(ieee80211_is_probe_resp(hdr->frame_control)))
+                txc->s.misc |= CARL9170_TX_SUPER_MISC_FILL_IN_TSF;
+
+        mac_tmp = cpu_to_le16(AR9170_TX_MAC_HW_DURATION |
+                              AR9170_TX_MAC_BACKOFF);
+        mac_tmp |= cpu_to_le16((hw_queue << AR9170_TX_MAC_QOS_S) &&
+                               AR9170_TX_MAC_QOS);
+
         no_ack = !!(info->flags & IEEE80211_TX_CTL_NO_ACK);
+        if (unlikely(no_ack))
+                mac_tmp |= cpu_to_le16(AR9170_TX_MAC_NO_ACK);
 
         if (info->control.hw_key) {
-                icv = info->control.hw_key->icv_len;
+                len += info->control.hw_key->icv_len;
 
                 switch (info->control.hw_key->cipher) {
                 case WLAN_CIPHER_SUITE_WEP40:
                 case WLAN_CIPHER_SUITE_WEP104:
                 case WLAN_CIPHER_SUITE_TKIP:
-                        keytype = AR9170_TX_MAC_ENCR_RC4;
+                        mac_tmp |= cpu_to_le16(AR9170_TX_MAC_ENCR_RC4);
                         break;
                 case WLAN_CIPHER_SUITE_CCMP:
-                        keytype = AR9170_TX_MAC_ENCR_AES;
+                        mac_tmp |= cpu_to_le16(AR9170_TX_MAC_ENCR_AES);
                         break;
                 default:
                         WARN_ON(1);
@@ -814,48 +835,58 @@ static int carl9170_tx_prepare(struct ar9170 *ar, struct sk_buff *skb)
                 }
         }
 
-        BUILD_BUG_ON(AR9170_MAX_VIRTUAL_MAC >
-                ((CARL9170_TX_SUPER_MISC_VIF_ID >>
-                 CARL9170_TX_SUPER_MISC_VIF_ID_S) + 1));
-
-        txc->s.len = cpu_to_le16(len + sizeof(*txc));
-        txc->f.length = cpu_to_le16(len + icv + 4);
-        SET_VAL(CARL9170_TX_SUPER_MISC_VIF_ID, txc->s.misc,
-                cvif ? cvif->id : 0);
+        ampdu = !!(info->flags & IEEE80211_TX_CTL_AMPDU);
+        if (ampdu) {
+                unsigned int density, factor;
 
-        txc->f.mac_control = cpu_to_le16(AR9170_TX_MAC_HW_DURATION |
-                                         AR9170_TX_MAC_BACKOFF);
+                if (unlikely(!sta || !cvif))
+                        goto err_out;
 
-        SET_VAL(CARL9170_TX_SUPER_MISC_QUEUE, txc->s.misc, hw_queue);
+                factor = min_t(unsigned int, 1u,
+                         info->control.sta->ht_cap.ampdu_factor);
 
-        txc->f.mac_control |= cpu_to_le16(hw_queue << AR9170_TX_MAC_QOS_S);
-        txc->f.mac_control |= cpu_to_le16(keytype);
-        txc->f.phy_control = cpu_to_le32(0);
+                density = info->control.sta->ht_cap.ampdu_density;
 
-        if (no_ack)
-                txc->f.mac_control |= cpu_to_le16(AR9170_TX_MAC_NO_ACK);
+                if (density) {
+                        /*
+                         * Watch out!
+                         *
+                         * Otus uses slightly different density values than
+                         * those from the 802.11n spec.
+                         */
 
-        if (info->flags & IEEE80211_TX_CTL_SEND_AFTER_DTIM)
-                txc->s.misc |= CARL9170_TX_SUPER_MISC_CAB;
+                        density = max_t(unsigned int, density + 1, 7u);
+                }
 
-        txrate = &info->control.rates[0];
-        if (carl9170_tx_rts_check(ar, txrate, ampdu, no_ack))
-                txc->f.mac_control |= cpu_to_le16(AR9170_TX_MAC_PROT_RTS);
-        else if (carl9170_tx_cts_check(ar, txrate))
-                txc->f.mac_control |= cpu_to_le16(AR9170_TX_MAC_PROT_CTS);
+                SET_VAL(CARL9170_TX_SUPER_AMPDU_DENSITY,
+                        txc->s.ampdu_settings, density);
 
-        SET_VAL(CARL9170_TX_SUPER_RI_TRIES, txc->s.ri[0], txrate->count);
-        txc->f.phy_control |= carl9170_tx_physet(ar, info, txrate);
+                SET_VAL(CARL9170_TX_SUPER_AMPDU_FACTOR,
+                        txc->s.ampdu_settings, factor);
 
-        if (info->flags & IEEE80211_TX_CTL_AMPDU) {
-                for (i = 1; i < CARL9170_TX_MAX_RATES; i++) {
+                for (i = 0; i < CARL9170_TX_MAX_RATES; i++) {
                         txrate = &info->control.rates[i];
-                        if (txrate->idx >= 0)
+                        if (txrate->idx >= 0) {
+                                txc->s.ri[i] =
+                                        CARL9170_TX_SUPER_RI_AMPDU;
+
+                                if (WARN_ON(!(txrate->flags &
+                                              IEEE80211_TX_RC_MCS))) {
+                                        /*
+                                         * Not sure if it's even possible
+                                         * to aggregate non-ht rates with
+                                         * this HW.
+                                         */
+                                        goto err_out;
+                                }
                                 continue;
+                        }
 
                         txrate->idx = 0;
                         txrate->count = ar->hw->max_rate_tries;
                 }
+
+                mac_tmp |= cpu_to_le16(AR9170_TX_MAC_AGGR);
         }
 
         /*
@@ -878,57 +909,21 @@ static int carl9170_tx_prepare(struct ar9170 *ar, struct sk_buff *skb)
                         txc->s.ri[i] |= (AR9170_TX_MAC_PROT_CTS <<
                                 CARL9170_TX_SUPER_RI_ERP_PROT_S);
 
-                /*
-                 * unaggregated fallback, in case aggregation
-                 * proves to be unsuccessful and unreliable.
-                 */
-                if (ampdu && i < 3)
-                        txc->s.ri[i] |= CARL9170_TX_SUPER_RI_AMPDU;
-
                 txc->s.rr[i - 1] = carl9170_tx_physet(ar, info, txrate);
         }
 
-        if (ieee80211_is_probe_resp(hdr->frame_control))
-                txc->s.misc |= CARL9170_TX_SUPER_MISC_FILL_IN_TSF;
-
-        if (ampdu) {
-                unsigned int density, factor;
-
-                if (unlikely(!sta || !cvif))
-                        goto err_out;
-
-                density = info->control.sta->ht_cap.ampdu_density;
-                factor = info->control.sta->ht_cap.ampdu_factor;
-
-                if (density) {
-                        /*
-                         * Watch out!
-                         *
-                         * Otus uses slightly different density values than
-                         * those from the 802.11n spec.
-                         */
-
-                        density = max_t(unsigned int, density + 1, 7u);
-                }
-
-                factor = min_t(unsigned int, 1u, factor);
-
-                SET_VAL(CARL9170_TX_SUPER_AMPDU_DENSITY,
-                        txc->s.ampdu_settings, density);
+        txrate = &info->control.rates[0];
+        SET_VAL(CARL9170_TX_SUPER_RI_TRIES, txc->s.ri[0], txrate->count);
 
-                SET_VAL(CARL9170_TX_SUPER_AMPDU_FACTOR,
-                        txc->s.ampdu_settings, factor);
+        if (carl9170_tx_rts_check(ar, txrate, ampdu, no_ack))
+                mac_tmp |= cpu_to_le16(AR9170_TX_MAC_PROT_RTS);
+        else if (carl9170_tx_cts_check(ar, txrate))
+                mac_tmp |= cpu_to_le16(AR9170_TX_MAC_PROT_CTS);
 
-                if (info->control.rates[0].flags & IEEE80211_TX_RC_MCS) {
-                        txc->f.mac_control |= cpu_to_le16(AR9170_TX_MAC_AGGR);
-                } else {
-                        /*
-                         * Not sure if it's even possible to aggregate
-                         * non-ht rates with this HW.
-                         */
-                        WARN_ON_ONCE(1);
-                }
-        }
+        txc->s.len = cpu_to_le16(skb->len);
+        txc->f.length = cpu_to_le16(len + FCS_LEN);
+        txc->f.mac_control = mac_tmp;
+        txc->f.phy_control = carl9170_tx_physet(ar, info, txrate);
 
         arinfo = (void *)info->rate_driver_data;
         arinfo->timeout = jiffies;