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SubjectRe: [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@ooseel.net>
>> ---
>> 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@ooseel.net/
>> ---
>> 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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