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Date: Sun, 18 Dec 2022 01:18:51 +0900
From: Leesoo Ahn <lsahn@...eel.net>
To: lsahn@...eel.net
Cc: Oliver Neukum <oneukum@...e.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] usbnet: jump to rx_cleanup case instead of calling skb_queue_tail
The current source pushes skb into dev->done queue by calling
skb_queue_tail() and then, call skb_dequeue() to pop for rx_cleanup state
to free urb and skb next in usbnet_bh().
It wastes CPU resource with extra instructions. Instead, use return values
jumping to rx_cleanup case directly to free them. Therefore calling
skb_queue_tail() and skb_dequeue() is not necessary.
The follows are just showing difference between calling skb_queue_tail()
and using return values jumping to rx_cleanup state directly in usbnet_bh()
in Arm64 instructions with perf tool.
----------- calling skb_queue_tail() -----------
│ if (!(dev->driver_info->flags & FLAG_RX_ASSEMBLE))
7.58 │248: ldr x0, [x20, #16]
2.46 │24c: ldr w0, [x0, #8]
1.64 │250: ↑ tbnz w0, #14, 16c
│ dev->net->stats.rx_errors++;
0.57 │254: ldr x1, [x20, #184]
1.64 │258: ldr x0, [x1, #336]
2.65 │25c: add x0, x0, #0x1
│260: str x0, [x1, #336]
│ skb_queue_tail(&dev->done, skb);
0.38 │264: mov x1, x19
│268: mov x0, x21
2.27 │26c: → bl skb_queue_tail
0.57 │270: ↑ b 44 // branch to call skb_dequeue()
----------- jumping to rx_cleanup state -----------
│ if (!(dev->driver_info->flags & FLAG_RX_ASSEMBLE))
1.69 │25c: ldr x0, [x21, #16]
4.78 │260: ldr w0, [x0, #8]
3.28 │264: ↑ tbnz w0, #14, e4 // jump to 'rx_cleanup' state
│ dev->net->stats.rx_errors++;
0.09 │268: ldr x1, [x21, #184]
2.72 │26c: ldr x0, [x1, #336]
3.37 │270: add x0, x0, #0x1
0.09 │274: str x0, [x1, #336]
0.66 │278: ↑ b e4 // branch to 'rx_cleanup' state
Signed-off-by: Leesoo Ahn <lsahn@...eel.net>
---
drivers/net/usb/usbnet.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 64a9a80b2309..924392a37297 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -555,7 +555,7 @@ static int rx_submit (struct usbnet *dev, struct urb *urb, gfp_t flags)
/*-------------------------------------------------------------------------*/
-static inline void rx_process (struct usbnet *dev, struct sk_buff *skb)
+static inline int rx_process(struct usbnet *dev, struct sk_buff *skb)
{
if (dev->driver_info->rx_fixup &&
!dev->driver_info->rx_fixup (dev, skb)) {
@@ -576,11 +576,11 @@ static inline void rx_process (struct usbnet *dev, struct sk_buff *skb)
netif_dbg(dev, rx_err, dev->net, "rx length %d\n", skb->len);
} else {
usbnet_skb_return(dev, skb);
- return;
+ return 0;
}
done:
- skb_queue_tail(&dev->done, skb);
+ return -1;
}
/*-------------------------------------------------------------------------*/
@@ -1528,13 +1528,14 @@ static void usbnet_bh (struct timer_list *t)
entry = (struct skb_data *) skb->cb;
switch (entry->state) {
case rx_done:
- entry->state = rx_cleanup;
- rx_process (dev, skb);
+ if (rx_process(dev, skb))
+ goto cleanup;
continue;
case tx_done:
kfree(entry->urb->sg);
fallthrough;
case rx_cleanup:
+cleanup:
usb_free_urb (entry->urb);
dev_kfree_skb (skb);
continue;
--
2.34.1
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