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Commit 59559f27 authored by Manu Gautam's avatar Manu Gautam Committed by Gerrit - the friendly Code Review server
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USB: u_ether: Align TX buffers to improve DL throughput 



USB2 controller's DMA performance degrades when request buffers
are not aligned to 4 bytes. Driver is already taking care of RX
buffers. Add changes to align TX skb if skb data is not starting
at aligned address. Though it adds penalty of memcpy but still
improves performance by overcoming USB DMA bottleneck.
Buffers are currently already aligned if RNDIS aggregation is
used. Issue is seen only with ECM or RNDIS with aggregation
disabled. RNDIS DL aggregation can be disabled using:
-> echo 0 > /sys/module/g_android/parameters/rndis_dl_max_pkt_per_xfer
While at it, also double DL buffers to 20 from 10, as USB
interrupt is enabled for every 5th buffer. This often causes
under runs if USB controller also uses interrupt latency >= 1msec
with data transfer >= 120Mbps and packet size = 1500 bytes.

Change-Id: Idfd960dff73359fda8c9bc66f7056bafe2dc3265
Signed-off-by: default avatarManu Gautam <mgautam@codeaurora.org>
Signed-off-by: default avatarAjay Agarwal <ajaya@codeaurora.org>
parent 616d2ea4

drivers/usb/gadget/function/u_ether.c

+16 −8
Original line number Original line Diff line number Diff line
@@ -129,7 +129,7 @@ static void uether_debugfs_exit(struct eth_dev *dev); 
 * of interconnect, data can be very bursty. tx_qmult is the

 * of interconnect, data can be very bursty. tx_qmult is the

 * additional multipler on qmult.

 * additional multipler on qmult.

 */

 */

static unsigned int tx_qmult = 1;

static unsigned int tx_qmult = 2;

module_param(tx_qmult, uint, 0644);

module_param(tx_qmult, uint, 0644);

MODULE_PARM_DESC(tx_qmult, "Additional queue length multiplier for tx");

MODULE_PARM_DESC(tx_qmult, "Additional queue length multiplier for tx");
@@ -857,21 +857,28 @@ static netdev_tx_t eth_start_xmit(struct sk_buff *skb, 
		dev->tx_skb_hold_count = 0;

		dev->tx_skb_hold_count = 0;

		spin_unlock_irqrestore(&dev->lock, flags);

		spin_unlock_irqrestore(&dev->lock, flags);

	} else {

	} else {

		bool do_align = false;



		/* Check if TX buffer should be aligned before queuing to hw */

		if (dev->gadget->is_chipidea &&

		    !IS_ALIGNED((size_t)skb->data, 4))

			do_align = true;



		/*

		/*

		 * Some UDC requires allocation of some extra bytes for

		 * Some UDC requires allocation of some extra bytes for

		 * TX buffer due to hardware requirement. Check if extra

		 * TX buffer due to hardware requirement. Check if extra

		 * bytes are already there, otherwise allocate new buffer

		 * bytes are already there, otherwise allocate new buffer

		 * with extra bytes and do memcpy.

		 * with extra bytes and do memcpy to align skb as well.

		 */

		 */

		length = skb->len;

		if (dev->gadget->extra_buf_alloc)

		if (dev->gadget->extra_buf_alloc)

			extra_alloc = EXTRA_ALLOCATION_SIZE_U_ETH;

			extra_alloc = EXTRA_ALLOCATION_SIZE_U_ETH;

		tail_room = skb_tailroom(skb);

		tail_room = skb_tailroom(skb);

		if (tail_room < extra_alloc) {

		if (do_align || tail_room < extra_alloc) {

			pr_debug("%s: tail_room  %d less than %d\n", __func__,

			pr_debug("%s:align skb and update tail_room %d to %d\n",

					tail_room, extra_alloc);

					__func__, tail_room, extra_alloc);

			new_skb = skb_copy_expand(skb, 0, extra_alloc -

			tail_room = extra_alloc;

					tail_room, GFP_ATOMIC);

			new_skb = skb_copy_expand(skb, 0, tail_room,

						  GFP_ATOMIC);

			if (!new_skb)

			if (!new_skb)

				return -ENOMEM;

				return -ENOMEM;

			dev_kfree_skb_any(skb);

			dev_kfree_skb_any(skb);
@@ -879,6 +886,7 @@ static netdev_tx_t eth_start_xmit(struct sk_buff *skb, 
			dev->skb_expand_cnt++;

			dev->skb_expand_cnt++;

		}

		}





		length = skb->len;

		req->buf = skb->data;

		req->buf = skb->data;

		req->context = skb;

		req->context = skb;

	}

	}