btw. it looks like irq throttling in the same file:
@@ -598,9 +599,10 @@ static netdev_tx_t eth_start_xmit(struct sk_buff *skb,
- /* throttle highspeed IRQ rate back slightly */
+ /* throttle high/super speed IRQ rate back slightly */
if (gadget_is_dualspeed(dev->gadget))
- req->no_interrupt = (dev->gadget->speed == USB_SPEED_HIGH)
+ req->no_interrupt = (dev->gadget->speed == USB_SPEED_HIGH ||
+ dev->gadget->speed == USB_SPEED_SUPER)
should also be fixed to be >= SUPER and not ==.
On Thu, Aug 6, 2020 at 10:29 AM Maciej Żenczykowski
<zenczykowski@xxxxxxxxx> wrote:
>
> On Thu, Aug 6, 2020 at 9:17 AM Lorenzo Colitti <lorenzo@xxxxxxxxxx> wrote:
> >
> > The u_ether driver has a qmult setting that multiplies the
> > transmit queue length (which by default is 2).
> >
> > The intent is that it should be enabled at high/super speed, but
> > because the code does not explicitly check for USB_SUPER_PLUS,
> > it is disabled at that speed.
> >
> > Fix this by ensuring that the queue multiplier is enabled for any
> > wired link at high speed or above. Using >= for USB_SPEED_*
> > constants seems correct because it is what the gadget_is_xxxspeed
> > functions do.
> >
> > The queue multiplier substantially helps performance at higher
> > speeds. On a direct SuperSpeed Plus link to a Linux laptop,
> > iperf3 single TCP stream:
> >
> > Before (qmult=1): 1.3 Gbps
> > After (qmult=5): 3.2 Gbps
> >
> > Signed-off-by: Lorenzo Colitti <lorenzo@xxxxxxxxxx>
> > ---
> > drivers/usb/gadget/function/u_ether.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
> > index c3cc6bd14e..31ea76adcc 100644
> > --- a/drivers/usb/gadget/function/u_ether.c
> > +++ b/drivers/usb/gadget/function/u_ether.c
> > @@ -93,7 +93,7 @@ struct eth_dev {
> > static inline int qlen(struct usb_gadget *gadget, unsigned qmult)
> > {
> > if (gadget_is_dualspeed(gadget) && (gadget->speed == USB_SPEED_HIGH ||
> > - gadget->speed == USB_SPEED_SUPER))
> > + gadget->speed >= USB_SPEED_SUPER))
> > return qmult * DEFAULT_QLEN;
> > else
> > return DEFAULT_QLEN;
> > --
> > 2.28.0.163.g6104cc2f0b6-goog
> >
>
> Reviewed-by: Maciej Żenczykowski <maze@xxxxxxxxxx>
>
> Though I think this probably deserves a fixes tag of some sort.
> Probably:
>
> Fixes: 04617db7aa68 ("usb: gadget: add SS descriptors to Ethernet gadget")
>
> since that's the commit that did:
>
> -MODULE_PARM_DESC(qmult, "queue length multiplier at high speed");
> +MODULE_PARM_DESC(qmult, "queue length multiplier at high/super speed");
>
> ...
>
> -/* for dual-speed hardware, use deeper queues at highspeed */
> +/* for dual-speed hardware, use deeper queues at high/super speed */
> static inline int qlen(struct usb_gadget *gadget)
> {
> - if (gadget_is_dualspeed(gadget) && gadget->speed == USB_SPEED_HIGH)
> + if (gadget_is_dualspeed(gadget) && (gadget->speed == USB_SPEED_HIGH ||
> + gadget->speed == USB_SPEED_SUPER))
> return qmult * DEFAULT_QLEN;
> else
> return DEFAULT_QLEN;
