[PATCH] usb: gadget: u_ether: enable qmult on SuperSpeed Plus as well

[PATCH] usb: gadget: u_ether: enable qmult on SuperSpeed Plus as well

[Lorenzo Colitti]

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@google.com>
---
 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

Re: [PATCH] usb: gadget: u_ether: enable qmult on SuperSpeed Plus as well

[Maciej Żenczykowski]

On Thu, Aug 6, 2020 at 9:17 AM Lorenzo Colitti <lorenzo@google.com> 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@google.com>
> ---
>  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@google.com>

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;

Re: [PATCH] usb: gadget: u_ether: enable qmult on SuperSpeed Plus as well

[Maciej Żenczykowski]

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@gmail.com> wrote:
>
> On Thu, Aug 6, 2020 at 9:17 AM Lorenzo Colitti <lorenzo@google.com> 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@google.com>
> > ---
> >  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@google.com>
>
> 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;

Re: [PATCH] usb: gadget: u_ether: enable qmult on SuperSpeed Plus as well

[Lorenzo Colitti]

> Reviewed-by: Maciej Żenczykowski <maze@google.com>
>
> 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");

Thanks for the review. Added Fixes: tag in v2.

Re: [PATCH] usb: gadget: u_ether: enable qmult on SuperSpeed Plus as well

[Lorenzo Colitti]

On Fri, Aug 7, 2020 at 2:41 AM Maciej Żenczykowski
<zenczykowski@gmail.com> wrote:
> 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 ==.

That code was removed by fd9afd3cbe40 ("usb: gadget: u_ether: remove
interrupt throttling").