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

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Message-ID: <lsq.1487198500.520011670@decadent.org.uk>
Date:   Wed, 15 Feb 2017 22:41:40 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Felipe Balbi" <felipe.balbi@...ux.intel.com>,
        "David Miller" <davem@...emloft.net>,
        "Ville Syrjälä" <ville.syrjala@...ux.intel.com>
Subject: [PATCH 3.16 196/306] usb: gadget: u_ether: remove interrupt
 throttling

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

------------------

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>
[bwh: Backported to 3.16: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- 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) {
 	default: