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

[Leesoo Ahn]

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