[PATCH 3.16 196/306] usb: gadget: u_ether: remove interrupt throttling

From: Ben Hutchings
Date: Wed Feb 15 2017 - 18:09:50 EST

3.16.40-rc1 review patch. If anyone has any objections, please let me know.


From: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>

commit fd9afd3cbe404998d732be6cc798f749597c5114 upstream.

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.

Reported-by: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>
Tested-by: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>
Suggested-by: David Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
--- a/drivers/usb/gadget/u_ether.c
+++ b/drivers/usb/gadget/u_ether.c
@@ -583,13 +583,6 @@ static netdev_tx_t eth_start_xmit(struct

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)
- ? ((atomic_read(&dev->tx_qlen) % dev->qmult) != 0)
- : 0;
retval = usb_ep_queue(in, req, GFP_ATOMIC);
switch (retval) {