Re: [PATCH] usb: gadget: u_ether: remove interrupt throttling

[Peter Chen <hzpeterchen@gmail.com>]

On Tue, Nov 01, 2016 at 01:29:59PM +0200, Felipe Balbi wrote:
> According to Dave Miller "the networking stack has a
> hard requirement that all SKBs which are transmitted
> must have their completion signalled in a fininte
> amount of time. This is because, until the SKB is
> freed by the driver, it holds onto socket,
> netfilter, and other subsystem resources."
> 
> In summary, this means that using TX IRQ throttling
> for the networking gadgets is, at least, complex and
> we should avoid it for the time being.
> 
> Cc: <stable@vger.kernel.org>
> Reported-by: Ville Syrj�l� <ville.syrjala@linux.intel.com>
> Suggested-by: David Miller <davem@davemloft.net>
> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
> ---
>  drivers/usb/gadget/function/u_ether.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
> index f4a640216913..119a2e5848e8 100644
> --- a/drivers/usb/gadget/function/u_ether.c
> +++ b/drivers/usb/gadget/function/u_ether.c
> @@ -589,14 +589,6 @@ static netdev_tx_t eth_start_xmit(struct sk_buff *skb,
>  
>  	req->length = length;
>  
> -	/* throttle high/super speed IRQ rate back slightly */
> -	if (gadget_is_dualspeed(dev->gadget))
> -		req->no_interrupt = (((dev->gadget->speed == USB_SPEED_HIGH ||
> -				       dev->gadget->speed == USB_SPEED_SUPER)) &&
> -					!list_empty(&dev->tx_reqs))
> -			? ((atomic_read(&dev->tx_qlen) % dev->qmult) != 0)
> -			: 0;
> -
>  	retval = usb_ep_queue(in, req, GFP_ATOMIC);
>  	switch (retval) {
>  	default:
> -- 

Felipe, it may increase cpu utilization since more interrupts will be there,
it may affect the SoC which has lower cpu frequency. This code existed
many years, why this problem has only reported at dwc3 recently?

-- 

Best Regards,
Peter Chen