Date:	Fri, 07 Sep 2012 09:35:46 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Bjørn Mork <bjorn@...k.no>,
	alexey.orishko@...ricsson.com, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: changing usbnet's API to better deal with cdc-ncm

On Friday 07 September 2012 11:55:53 Ming Lei wrote:
> On Fri, Sep 7, 2012 at 1:56 AM, Oliver Neukum <oneukum@...e.de> wrote:
> > On Friday 07 September 2012 00:09:13 Ming Lei wrote:
> >> On Thu, Sep 6, 2012 at 4:30 PM, Bjørn Mork <bjorn@...k.no> wrote:
> >> > Ming Lei <tom.leiming@...il.com> writes:
> >
> >> >> Looks the introduced .tx_bundle is not necessary since .tx_fixup is OK.
> >> >
> >> > The minidriver does not have any information about tx in progress.  The
> >>
> >> Inside .tx_fixup, the low level driver will get the tx progress information.
> >
> > That information changes after tx_fixup
> 
> You mean the low level drive can't see if the later transmission
> for the aggregated frame is successful?  If so, there is no any complete

Not successful, necessary.

> notification to all low level drivers (with aggregation capability
> or not) now, isn't there?

There doesn't need to be.

> > Well, that is the mistake. Using a timer is a bad idea.
> 
> Why is a bad idea?  Without a timer, how can usbnet or
> low level driver aggregate the later coming transmit frames to
> form a biger aggregated frame?

By registering demand in an abstract sense. The timer makes sense
only when no other buffers are being transfered.

The timer means that we transmit if no other more packages are coming
down from the upper layers. Now, either the device is still busy or it is not.
While it is busy, we might just as well wait, because the upper layer may
change its mind.
If the device is not busy we worsen latency by waiting for the timer.

In addition the timer causes complications with recursing into usbnet
and hassle with suspend/resume and disconnection.

> >> If we can abstract some common things about aggregation, it should be
> >> meaningful. As far as I know, most of aggregation protocol is very different,
> >> so almost all aggregation work is only done by low level driver, such as
> >> cdc_ncm.
> >>
> >> If we want to implement some aggregation framework, maybe below is
> >> one solution, correct me if it is wrong.
> >
> > It isn't so much wrong as incomplete.
> >
> > It seems to me we can have
> >
> > - can queue, buffer not full -> do nothing more
> 
> As I said above, without a timeout timer, the queued skb
> might not be sent out even some long time passed if no
> frame comes later.

Therefore we check whether the device is still busy.

> So could you add the wait for more mechanism to your patch
> for further discussion?

I am attaching a version that is algorithmically complete
except for error handling.

> > - can queue, buffer full -> transmit
> > - cannot queue, buffer full -> transmit and then try again to queue
> 
> This might not happen, the buffer full should have been observed
> in last xmit path.

Possibly, but the driver cannot know in advance how large the next package
will be.

	Reagrds
		Oliver

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 4cd582a..56ef743 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -135,9 +135,6 @@ struct cdc_ncm_ctx {
 	u16 connected;
 };
 
-static void cdc_ncm_txpath_bh(unsigned long param);
-static void cdc_ncm_tx_timeout_start(struct cdc_ncm_ctx *ctx);
-static enum hrtimer_restart cdc_ncm_tx_timer_cb(struct hrtimer *hr_timer);
 static struct usb_driver cdc_ncm_driver;
 
 static void
@@ -464,10 +461,6 @@ static int cdc_ncm_bind(struct usbnet *dev, struct usb_interface *intf)
 	if (ctx == NULL)
 		return -ENODEV;
 
-	hrtimer_init(&ctx->tx_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
-	ctx->tx_timer.function = &cdc_ncm_tx_timer_cb;
-	ctx->bh.data = (unsigned long)ctx;
-	ctx->bh.func = cdc_ncm_txpath_bh;
 	atomic_set(&ctx->stop, 0);
 	spin_lock_init(&ctx->mtx);
 	ctx->netdev = dev->net;
@@ -650,7 +643,7 @@ static void cdc_ncm_zero_fill(u8 *ptr, u32 first, u32 end, u32 max)
 	memset(ptr + first, 0, end - first);
 }
 
-static struct sk_buff *
+static int
 cdc_ncm_fill_tx_frame(struct cdc_ncm_ctx *ctx, struct sk_buff *skb)
 {
 	struct sk_buff *skb_out;
@@ -659,12 +652,7 @@ cdc_ncm_fill_tx_frame(struct cdc_ncm_ctx *ctx, struct sk_buff *skb)
 	u32 last_offset;
 	u16 n = 0, index;
 	u8 ready2send = 0;
-
-	/* if there is a remaining skb, it gets priority */
-	if (skb != NULL)
-		swap(skb, ctx->tx_rem_skb);
-	else
-		ready2send = 1;
+	u8 error = 0;
 
 	/*
 	 * +----------------+
@@ -690,7 +678,7 @@ cdc_ncm_fill_tx_frame(struct cdc_ncm_ctx *ctx, struct sk_buff *skb)
 				dev_kfree_skb_any(skb);
 				ctx->netdev->stats.tx_dropped++;
 			}
-			goto exit_no_skb;
+			return -EBUSY;
 		}
 
 		/* make room for NTH and NDP */
@@ -719,28 +707,15 @@ cdc_ncm_fill_tx_frame(struct cdc_ncm_ctx *ctx, struct sk_buff *skb)
 		/* compute maximum buffer size */
 		rem = ctx->tx_max - offset;
 
-		if (skb == NULL) {
-			skb = ctx->tx_rem_skb;
-			ctx->tx_rem_skb = NULL;
-
-			/* check for end of skb */
-			if (skb == NULL)
-				break;
-		}
-
 		if (skb->len > rem) {
 			if (n == 0) {
 				/* won't fit, MTU problem? */
 				dev_kfree_skb_any(skb);
 				skb = NULL;
 				ctx->netdev->stats.tx_dropped++;
+				error = 1;
 			} else {
-				/* no room for skb - store for later */
-				if (ctx->tx_rem_skb != NULL) {
-					dev_kfree_skb_any(ctx->tx_rem_skb);
-					ctx->netdev->stats.tx_dropped++;
-				}
-				ctx->tx_rem_skb = skb;
+
 				skb = NULL;
 				ready2send = 1;
 			}
@@ -768,13 +743,6 @@ cdc_ncm_fill_tx_frame(struct cdc_ncm_ctx *ctx, struct sk_buff *skb)
 		skb = NULL;
 	}
 
-	/* free up any dangling skb */
-	if (skb != NULL) {
-		dev_kfree_skb_any(skb);
-		skb = NULL;
-		ctx->netdev->stats.tx_dropped++;
-	}
-
 	ctx->tx_curr_frame_num = n;
 
 	if (n == 0) {
@@ -791,9 +759,7 @@ cdc_ncm_fill_tx_frame(struct cdc_ncm_ctx *ctx, struct sk_buff *skb)
 		ctx->tx_curr_skb = skb_out;
 		ctx->tx_curr_offset = offset;
 		ctx->tx_curr_last_offset = last_offset;
-		/* set the pending count */
-		if (n < CDC_NCM_RESTART_TIMER_DATAGRAM_CNT)
-			ctx->tx_timer_pending = CDC_NCM_TIMER_PENDING_CNT;
+
 		goto exit_no_skb;
 
 	} else {
@@ -874,71 +840,37 @@ cdc_ncm_fill_tx_frame(struct cdc_ncm_ctx *ctx, struct sk_buff *skb)
 	/* return skb */
 	ctx->tx_curr_skb = NULL;
 	ctx->netdev->stats.tx_packets += ctx->tx_curr_frame_num;
-	return skb_out;
 
-exit_no_skb:
-	/* Start timer, if there is a remaining skb */
-	if (ctx->tx_curr_skb != NULL)
-		cdc_ncm_tx_timeout_start(ctx);
-	return NULL;
-}
-
-static void cdc_ncm_tx_timeout_start(struct cdc_ncm_ctx *ctx)
-{
-	/* start timer, if not already started */
-	if (!(hrtimer_active(&ctx->tx_timer) || atomic_read(&ctx->stop)))
-		hrtimer_start(&ctx->tx_timer,
-				ktime_set(0, CDC_NCM_TIMER_INTERVAL),
-				HRTIMER_MODE_REL);
-}
+	if (error)
+		return -EBUSY;
+	if (ready2send)
+		return -EBUSY;
+	else
+		return 0;
 
-static enum hrtimer_restart cdc_ncm_tx_timer_cb(struct hrtimer *timer)
-{
-	struct cdc_ncm_ctx *ctx =
-			container_of(timer, struct cdc_ncm_ctx, tx_timer);
+exit_no_skb:
 
-	if (!atomic_read(&ctx->stop))
-		tasklet_schedule(&ctx->bh);
-	return HRTIMER_NORESTART;
+	return -EAGAIN;
 }
 
-static void cdc_ncm_txpath_bh(unsigned long param)
+static int cdc_ncm_tx_bundle(struct usbnet *dev, struct sk_buff *skb, gfp_t flags)
 {
-	struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)param;
-
-	spin_lock_bh(&ctx->mtx);
-	if (ctx->tx_timer_pending != 0) {
-		ctx->tx_timer_pending--;
-		cdc_ncm_tx_timeout_start(ctx);
-		spin_unlock_bh(&ctx->mtx);
-	} else if (ctx->netdev != NULL) {
-		spin_unlock_bh(&ctx->mtx);
-		netif_tx_lock_bh(ctx->netdev);
-		usbnet_start_xmit(NULL, ctx->netdev);
-		netif_tx_unlock_bh(ctx->netdev);
-	}
+	int err;
+	struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
+	
+	err = cdc_ncm_fill_tx_frame(ctx, skb);
+	return err;
 }
 
 static struct sk_buff *
 cdc_ncm_tx_fixup(struct usbnet *dev, struct sk_buff *skb, gfp_t flags)
 {
-	struct sk_buff *skb_out;
 	struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
 
-	/*
-	 * The Ethernet API we are using does not support transmitting
-	 * multiple Ethernet frames in a single call. This driver will
-	 * accumulate multiple Ethernet frames and send out a larger
-	 * USB frame when the USB buffer is full or when a single jiffies
-	 * timeout happens.
-	 */
 	if (ctx == NULL)
 		goto error;
 
-	spin_lock_bh(&ctx->mtx);
-	skb_out = cdc_ncm_fill_tx_frame(ctx, skb);
-	spin_unlock_bh(&ctx->mtx);
-	return skb_out;
+	return ctx->tx_curr_skb;
 
 error:
 	if (skb != NULL)
@@ -1197,6 +1129,7 @@ static const struct driver_info cdc_ncm_info = {
 	.manage_power = cdc_ncm_manage_power,
 	.status = cdc_ncm_status,
 	.rx_fixup = cdc_ncm_rx_fixup,
+	.tx_bundle = cdc_ncm_tx_bundle,
 	.tx_fixup = cdc_ncm_tx_fixup,
 };
 
@@ -1211,6 +1144,7 @@ static const struct driver_info wwan_info = {
 	.manage_power = cdc_ncm_manage_power,
 	.status = cdc_ncm_status,
 	.rx_fixup = cdc_ncm_rx_fixup,
+	.tx_bundle = cdc_ncm_tx_bundle,
 	.tx_fixup = cdc_ncm_tx_fixup,
 };
 
diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 8531c1c..429b08b 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -86,6 +86,8 @@ static u8	node_id [ETH_ALEN];
 
 static const char driver_name [] = "usbnet";
 
+static void tx_complete(struct urb *urb);
+
 /* use ethtool to change the level for any given device */
 static int msg_level = -1;
 module_param (msg_level, int, 0);
@@ -1016,17 +1018,76 @@ skip_reset:
 		netdev_dbg(dev->net, "kevent done, flags = 0x%lx\n", dev->flags);
 }
 
+static int submit_next_bundle(struct usbnet *dev, struct sk_buff *skb)
+{
+	struct skb_data *entry;
+	int length = skb->len;
+	int retval;
+	struct driver_info *info = dev->driver_info;
+	struct urb *urb;
+
+	urb = usb_alloc_urb(0, GFP_ATOMIC);
+	if (!urb)
+		return -ENOMEM;
+
+	entry = (struct skb_data *) skb->cb;
+	entry->urb = urb;
+	entry->dev = dev;
+	entry->length = length;
+
+	usb_fill_bulk_urb (urb, dev->udev, dev->out,
+			skb->data, skb->len, tx_complete, skb);
+
+	/* don't assume the hardware handles USB_ZERO_PACKET
+	 * NOTE:  strictly conforming cdc-ether devices should expect
+	 * the ZLP here, but ignore the one-byte packet.
+	 * NOTE2: CDC NCM specification is different from CDC ECM when
+	 * handling ZLP/short packets, so cdc_ncm driver will make short
+	 * packet itself if needed.
+	 */
+	if (length % dev->maxpacket == 0) {
+		if (!(info->flags & FLAG_SEND_ZLP)) {
+			if (!(info->flags & FLAG_MULTI_PACKET)) {
+				urb->transfer_buffer_length++;
+				if (skb_tailroom(skb)) {
+					skb->data[skb->len] = 0;
+					__skb_put(skb, 1);
+				}
+			}
+		} else
+			urb->transfer_flags |= URB_ZERO_PACKET;
+	}
+
+	atomic_inc(&dev->tx_in_flight);
+	retval = usb_submit_urb(urb, GFP_ATOMIC);
+	if (retval < 0)
+		atomic_dec(&dev->tx_in_flight);
+	//FIXME: full error handling
+
+	return retval;
+}
 /*-------------------------------------------------------------------------*/
 
 static void tx_complete (struct urb *urb)
 {
 	struct sk_buff		*skb = (struct sk_buff *) urb->context;
+	struct sk_buff		*skb2;
 	struct skb_data		*entry = (struct skb_data *) skb->cb;
 	struct usbnet		*dev = entry->dev;
+	struct driver_info	*info = dev->driver_info;
+	int			in_flight;
 
+	in_flight = atomic_dec_return(&dev->tx_in_flight);
 	if (urb->status == 0) {
-		if (!(dev->driver_info->flags & FLAG_MULTI_PACKET))
+		if (!(dev->driver_info->flags & FLAG_MULTI_PACKET)) {
 			dev->net->stats.tx_packets++;
+		} else {
+			if (in_flight < 2) {
+				skb2 = info->tx_fixup(dev, NULL, GFP_ATOMIC);
+				if (skb2)
+					submit_next_bundle(dev, skb2);
+			}
+		}
 		dev->net->stats.tx_bytes += entry->length;
 	} else {
 		dev->net->stats.tx_errors++;
@@ -1089,23 +1150,50 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
 	struct urb		*urb = NULL;
 	struct skb_data		*entry;
 	struct driver_info	*info = dev->driver_info;
+	struct sk_buff		*skb_old = NULL;
 	unsigned long		flags;
 	int retval;
+	int transmit_now = 1;
+	int bundle_again = 0;
 
 	if (skb)
 		skb_tx_timestamp(skb);
 
+	/*
+	 * first we allow drivers to bundle packets together
+	 * maintainance of the buffer is the responsibility
+	 * of the lower layer
+	 */
+rebundle:
+	if (info->tx_bundle) {
+		bundle_again = 0;
+		retval = info->tx_bundle(dev, skb, GFP_ATOMIC);
+
+		switch (retval) {
+		case 0: /* the package has been bundled */
+			if (atomic_read(&dev->tx_in_flight) < 2)
+				transmit_now = 1;
+			else
+				transmit_now = 0;
+			break;
+		case -EAGAIN:
+			transmit_now = 1;
+			bundle_again = 1;
+			skb_old = skb;
+			break;
+		case -EBUSY:
+			transmit_now = 1;
+			break;
+		}
+	}
 	// some devices want funky USB-level framing, for
 	// win32 driver (usually) and/or hardware quirks
-	if (info->tx_fixup) {
+	if (transmit_now && info->tx_fixup) {
 		skb = info->tx_fixup (dev, skb, GFP_ATOMIC);
 		if (!skb) {
 			if (netif_msg_tx_err(dev)) {
 				netif_dbg(dev, tx_err, dev->net, "can't tx_fixup skb\n");
 				goto drop;
-			} else {
-				/* cdc_ncm collected packet; waits for more */
-				goto not_drop;
 			}
 		}
 	}
@@ -1164,14 +1252,17 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
 	}
 #endif
 
+	atomic_inc(&dev->tx_in_flight);
 	switch ((retval = usb_submit_urb (urb, GFP_ATOMIC))) {
 	case -EPIPE:
 		netif_stop_queue (net);
 		usbnet_defer_kevent (dev, EVENT_TX_HALT);
+		atomic_dec(&dev->tx_in_flight);
 		usb_autopm_put_interface_async(dev->intf);
 		break;
 	default:
 		usb_autopm_put_interface_async(dev->intf);
+		atomic_dec(&dev->tx_in_flight);
 		netif_dbg(dev, tx_err, dev->net,
 			  "tx: submit urb err %d\n", retval);
 		break;
@@ -1187,7 +1278,6 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
 		netif_dbg(dev, tx_err, dev->net, "drop, code %d\n", retval);
 drop:
 		dev->net->stats.tx_dropped++;
-not_drop:
 		if (skb)
 			dev_kfree_skb_any (skb);
 		usb_free_urb (urb);
@@ -1197,6 +1287,10 @@ not_drop:
 #ifdef CONFIG_PM
 deferred:
 #endif
+	if (bundle_again) {
+		skb = skb_old;
+		goto rebundle;
+	}
 	return NETDEV_TX_OK;
 }
 EXPORT_SYMBOL_GPL(usbnet_start_xmit);
@@ -1393,6 +1487,7 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
 	dev->delay.data = (unsigned long) dev;
 	init_timer (&dev->delay);
 	mutex_init (&dev->phy_mutex);
+	atomic_set(&dev->tx_in_flight, 0); 
 
 	dev->net = net;
 	strcpy (net->name, "usb%d");
diff --git a/include/linux/usb/usbnet.h b/include/linux/usb/usbnet.h
index f87cf62..bb2f622 100644
--- a/include/linux/usb/usbnet.h
+++ b/include/linux/usb/usbnet.h
@@ -33,6 +33,7 @@ struct usbnet {
 	wait_queue_head_t	*wait;
 	struct mutex		phy_mutex;
 	unsigned char		suspend_count;
+	atomic_t		tx_in_flight;
 
 	/* i/o info: pipes etc */
 	unsigned		in, out;
@@ -133,6 +134,12 @@ struct driver_info {
 	/* fixup rx packet (strip framing) */
 	int	(*rx_fixup)(struct usbnet *dev, struct sk_buff *skb);
 
+	/* bundle individual package for transmission as
+	 * larger package. This cannot sleep
+	 */
+	int	(*tx_bundle)(struct usbnet *dev,
+				struct sk_buff *skb, gfp_t flags);
+
 	/* fixup tx packet (add framing) */
 	struct sk_buff	*(*tx_fixup)(struct usbnet *dev,
 				struct sk_buff *skb, gfp_t flags);

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