Re: [PATCH v2] usbnet: optimize usbnet_bh() to reduce CPU load

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On 22. 12. 21. 15:32, Greg KH wrote:
On Wed, Dec 21, 2022 at 01:42:30PM +0900, Leesoo Ahn wrote:
The current source pushes skb into dev->done queue by calling
skb_queue_tail() and then pop it by calling skb_dequeue() to branch to
rx_cleanup state for freeing urb/skb in usbnet_bh(). It takes extra CPU
load, 2.21% (skb_queue_tail) as follows.

-   11.58%     0.26%  swapper          [k] usbnet_bh
    - 11.32% usbnet_bh
       - 6.43% skb_dequeue
            6.34% _raw_spin_unlock_irqrestore
       - 2.21% skb_queue_tail
            2.19% _raw_spin_unlock_irqrestore
       - 1.68% consume_skb
          - 0.97% kfree_skbmem
               0.80% kmem_cache_free
            0.53% skb_release_data

To reduce the extra CPU load use return values jumping to rx_cleanup
state directly to free them instead of calling skb_queue_tail() and
skb_dequeue() for push/pop respectively.

-    7.87%     0.25%  swapper          [k] usbnet_bh
    - 7.62% usbnet_bh
       - 4.81% skb_dequeue
            4.74% _raw_spin_unlock_irqrestore
       - 1.75% consume_skb
          - 0.98% kfree_skbmem
               0.78% kmem_cache_free
            0.58% skb_release_data
         0.53% smsc95xx_rx_fixup

Signed-off-by: Leesoo Ahn <lsahn@xxxxxxxxxx>
---
v2:
   - Replace goto label with return statement to reduce goto entropy
   - Add CPU load information by perf in commit message

v1 at:
   https://patchwork.kernel.org/project/netdevbpf/patch/20221217161851.829497-1-lsahn@xxxxxxxxxx/
---
  drivers/net/usb/usbnet.c | 19 +++++++++----------
  1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 64a9a80b2309..6e82fef90dd9 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -555,32 +555,30 @@ 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)) {
  		/* With RX_ASSEMBLE, rx_fixup() must update counters */
  		if (!(dev->driver_info->flags & FLAG_RX_ASSEMBLE))
  			dev->net->stats.rx_errors++;
-		goto done;
+		return 1;
"1" means that you processed 1 byte, not that this is an error, which is
what you want to say here, right?
No not at all..
Please return a negative error value
like I asked this to be changed to last time :(
Could you help me to decide the message type at this point please? I am confused.

The return value totally depends on how rx_fixup() is. For instance, in smsc95xx.c, smsc95xx_rx_fixup() function returns 0 in two cases that

1) frame size is greater than ETH_FRAME_LEN(1526 bytes) as follows

 1853             /* ETH_FRAME_LEN + 4(CRC) + 2(COE) + 4(Vlan) */
 1854             if (unlikely(size > (ETH_FRAME_LEN + 12))) {
 1855                 netif_dbg(dev, rx_err, dev->net,
 1856                       "size err header=0x%08x\n", header);
 1857                 return 0;
 1858             }

2) it is failed for skb allocation, but memory?

 1870             ax_skb = skb_clone(skb, GFP_ATOMIC);
 1871             if (unlikely(!ax_skb)) {
 1872                 netdev_warn(dev->net, "Error allocating skb\n");
 1873                 return 0;
 1874             }

I guess EPROTO or ENOMEM, one of them could be the value at the point but I have no ideas..

Best regards,
Leesoo




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