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

["Ville Syrjälä" <ville.syrjala@linux.intel.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>

Fixes laggy/hangy g_ether on my BYT FFRD8 tablet, caused by
commit 55a0237f8f47 ("usb: dwc3: gadget: use allocated/queued reqs for LST bit")

Tested-by: Ville Syrj�l� <ville.syrjala@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:
> -- 
> 2.10.1

-- 
Ville Syrj�l�
Intel OTC