Commit fb59bf28 authored by Leesoo Ahn's avatar Leesoo Ahn Committed by David S. Miller
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usbnet: optimize usbnet_bh() to reduce CPU load 



The current source pushes skb into dev-done queue by calling
skb_dequeue_tail() and then pop it by 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 to call helper function
usb_free_skb() to free the resources instead of calling skb_queue_tail()
and skb_dequeue() for push and 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: default avatarLeesoo Ahn <lsahn@ooseel.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 9cb8bae3

drivers/net/usb/usbnet.c

+17 −12
Original line number Diff line number Diff line
@@ -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 -EPROTO;

	}

	// else network stack removes extra byte if we forced a short packet



	/* all data was already cloned from skb inside the driver */

	if (dev->driver_info->flags & FLAG_MULTI_PACKET)

		goto done;

		return -EALREADY;



	if (skb->len < ETH_HLEN) {

		dev->net->stats.rx_errors++;

		dev->net->stats.rx_length_errors++;

		netif_dbg(dev, rx_err, dev->net, "rx length %d\n", skb->len);

	} else {

		usbnet_skb_return(dev, skb);

		return;

		return -EPROTO;

	}



done:

	skb_queue_tail(&dev->done, skb);

	usbnet_skb_return(dev, skb);

	return 0;

}



/*-------------------------------------------------------------------------*/
@@ -1514,6 +1512,14 @@ static int rx_alloc_submit(struct usbnet *dev, gfp_t flags) 
	return ret;

}



static inline void usb_free_skb(struct sk_buff *skb)

{

	struct skb_data *entry = (struct skb_data *)skb->cb;



	usb_free_urb(entry->urb);

	dev_kfree_skb(skb);

}



/*-------------------------------------------------------------------------*/



// tasklet (work deferred from completions, in_irq) or timer
@@ -1528,15 +1534,14 @@ 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))

				usb_free_skb(skb);

			continue;

		case tx_done:

			kfree(entry->urb->sg);

			fallthrough;

		case rx_cleanup:

			usb_free_urb (entry->urb);

			dev_kfree_skb (skb);

			usb_free_skb(skb);

			continue;

		default:

			netdev_dbg(dev->net, "bogus skb state %d\n", entry->state);