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;
