linux-kernel - [PATCH 3.10 121/319] usb: gadget: u_ether: remove interrupt throttling

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Date:   Sun,  5 Feb 2017 20:19:03 +0100
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 121/319] usb: gadget: u_ether: remove interrupt throttling

From: Felipe Balbi <felipe.balbi@...ux.intel.com>

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 Syrjälä <ville.syrjala@...ux.intel.com>
Tested-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
Suggested-by: David Miller <davem@...emloft.net>
Signed-off-by: Felipe Balbi <felipe.balbi@...ux.intel.com>
Signed-off-by: Willy Tarreau <w@....eu>
---
 drivers/usb/gadget/u_ether.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/drivers/usb/gadget/u_ether.c b/drivers/usb/gadget/u_ether.c
index aad066d..ef5c623 100644
--- a/drivers/usb/gadget/u_ether.c
+++ b/drivers/usb/gadget/u_ether.c
@@ -584,14 +584,6 @@ 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) % qmult) != 0)
-			: 0;
-
 	retval = usb_ep_queue(in, req, GFP_ATOMIC);
 	switch (retval) {
 	default:
-- 
2.8.0.rc2.1.gbe9624a