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SubjectRe: [PATCH v2] usbnet: optimize usbnet_bh() to reduce CPU load
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? Please return a negative error value
like I asked this to be changed to last time :(

thanks,

greg k-h

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