wifi: rtw88: usb: Copy instead of cloning the RX skb

"iperf3 -c 192.168.0.1 -R --udp -b 0" shows about 40% of datagrams
are lost. Many torrents don't download faster than 3 MiB/s, probably
because the Bittorrent protocol uses UDP. This is somehow related to
the use of skb_clone() in the RX path.

Don't use skb_clone(). Instead allocate a new skb for each 802.11 frame
received and copy the data from the big (32768 byte) skb.

With this patch, "iperf3 -c 192.168.0.1 -R --udp -b 0" shows only 1-2%
of datagrams are lost, and torrents can reach download speeds of 36
MiB/s.

Tested with RTL8812AU and RTL8822CU.

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/8c9d4f9d-ebd8-4dc0-a0c4-9ebe430521dd@gmail.com

diff --git a/drivers/net/wireless/realtek/rtw88/usb.c b/drivers/net/wireless/realtek/rtw88/usb.c
index be193c7add77a50b7e8b60b239df02ee63da39c0..28679d9cdffceae5a7be08ccf9ddbae82b921eeb 100644 (file)
--- a/drivers/net/wireless/realtek/rtw88/usb.c
+++ b/drivers/net/wireless/realtek/rtw88/usb.c
@@ -7,6 +7,7 @@
 #include <linux/mutex.h>
 #include "main.h"
 #include "debug.h"
+#include "mac.h"
 #include "reg.h"
 #include "tx.h"
 #include "rx.h"
@@ -547,49 +548,58 @@ static void rtw_usb_rx_handler(struct work_struct *work)
 {
        struct rtw_usb *rtwusb = container_of(work, struct rtw_usb, rx_work);
        struct rtw_dev *rtwdev = rtwusb->rtwdev;
-       const struct rtw_chip_info *chip = rtwdev->chip;
-       u32 pkt_desc_sz = chip->rx_pkt_desc_sz;
        struct ieee80211_rx_status rx_status;
-       u32 pkt_offset, next_pkt, urb_len;
        struct rtw_rx_pkt_stat pkt_stat;
-       struct sk_buff *next_skb;
+       struct sk_buff *rx_skb;
        struct sk_buff *skb;
+       u32 pkt_desc_sz = rtwdev->chip->rx_pkt_desc_sz;
+       u32 max_skb_len = pkt_desc_sz + PHY_STATUS_SIZE * 8 +
+                         IEEE80211_MAX_MPDU_LEN_VHT_11454;
+       u32 pkt_offset, next_pkt, skb_len;
        u8 *rx_desc;
        int limit;
 
        for (limit = 0; limit < 200; limit++) {
-               skb = skb_dequeue(&rtwusb->rx_queue);
-               if (!skb)
+               rx_skb = skb_dequeue(&rtwusb->rx_queue);
+               if (!rx_skb)
                        break;
 
                if (skb_queue_len(&rtwusb->rx_queue) >= RTW_USB_MAX_RXQ_LEN) {
                        dev_dbg_ratelimited(rtwdev->dev, "failed to get rx_queue, overflow\n");
-                       dev_kfree_skb_any(skb);
+                       dev_kfree_skb_any(rx_skb);
                        continue;
                }
 
-               urb_len = skb->len;
+               rx_desc = rx_skb->data;
 
                do {
-                       rx_desc = skb->data;
                        rtw_rx_query_rx_desc(rtwdev, rx_desc, &pkt_stat,
                                             &rx_status);
                        pkt_offset = pkt_desc_sz + pkt_stat.drv_info_sz +
                                     pkt_stat.shift;
 
-                       next_pkt = round_up(pkt_stat.pkt_len + pkt_offset, 8);
+                       skb_len = pkt_stat.pkt_len + pkt_offset;
+                       if (skb_len > max_skb_len) {
+                               rtw_dbg(rtwdev, RTW_DBG_USB,
+                                       "skipping too big packet: %u\n",
+                                       skb_len);
+                               goto skip_packet;
+                       }
 
-                       if (urb_len >= next_pkt + pkt_desc_sz)
-                               next_skb = skb_clone(skb, GFP_KERNEL);
-                       else
-                               next_skb = NULL;
+                       skb = alloc_skb(skb_len, GFP_KERNEL);
+                       if (!skb) {
+                               rtw_dbg(rtwdev, RTW_DBG_USB,
+                                       "failed to allocate RX skb of size %u\n",
+                                       skb_len);
+                               goto skip_packet;
+                       }
+
+                       skb_put_data(skb, rx_desc, skb_len);
 
                        if (pkt_stat.is_c2h) {
-                               skb_trim(skb, pkt_stat.pkt_len + pkt_offset);
                                rtw_fw_c2h_cmd_rx_irqsafe(rtwdev, pkt_offset, skb);
                        } else {
                                skb_pull(skb, pkt_offset);
-                               skb_trim(skb, pkt_stat.pkt_len);
                                rtw_update_rx_freq_for_invalid(rtwdev, skb,
                                                               &rx_status,
                                                               &pkt_stat);
@@ -598,12 +608,12 @@ static void rtw_usb_rx_handler(struct work_struct *work)
                                ieee80211_rx_irqsafe(rtwdev->hw, skb);
                        }
 
-                       skb = next_skb;
-                       if (skb)
-                               skb_pull(skb, next_pkt);
+skip_packet:
+                       next_pkt = round_up(skb_len, 8);
+                       rx_desc += next_pkt;
+               } while (rx_desc + pkt_desc_sz < rx_skb->data + rx_skb->len);
 
-                       urb_len -= next_pkt;
-               } while (skb);
+               dev_kfree_skb_any(rx_skb);
        }
 }