netdev - Re: [PATCH v2] usbnet: optimize usbnet

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Date:   Wed, 21 Dec 2022 07:32:34 +0100
From:   Greg KH <greg@...ah.com>
To:     Leesoo Ahn <lsahn@...eel.net>
Cc:     Oliver Neukum <oneukum@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [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@...eel.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