linux-kernel - Re: [PATCH] usb/gadget/function/u

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Message-ID: <55CD9E6D.4030109@topic.nl>
Date:	Fri, 14 Aug 2015 09:53:17 +0200
From:	Mike Looijmans <mike.looijmans@...ic.nl>
To:	<balbi@...com>, <gregkh@...uxfoundation.org>
CC:	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb/gadget/function/u_ether.c: Allow jumbo frames

ping...

More than a week has passed, haven't seen any response though. Any comments?


On 05-08-15 08:54, Mike Looijmans wrote:
> USB network adapters support Jumbo frames. The only thing blocking
> that feature is the code in the gadget driver that disposes of
> packets larger than 1518 bytes, and the limit on the ioctl to set
> the mtu.
>
> This patch relaxes these limits, and allows up to 15k frames sizes.
> The 15k value was chosen because 16k does not work on all platforms,
> and usingclose to 16k will result in allocating 5 or 8 4k pages to
> store the skb, wasting pages at no measurable performance gain.
>
> On a topic-miami board (Zynq-7000), iperf3 performance reports:
> MTU= 1500, PC-to-gadget: 139 Mbps, Gadget-to-PC: 116 Mbps
> MTU=15000, PC-to-gadget: 239 Mbps, Gadget-to-PC: 361 Mbps
>
> On boards with slower CPUs the performance improvement will be
> relatively much larger, e.g. an OMAP-L138 increased from 40 to
> 220 Mbps using a similar patch on an  2.6.37 kernel.
>
> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
> ---
>   drivers/usb/gadget/function/u_ether.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_ether.c b/drivers/usb/gadget/function/u_ether.c
> index f1fd777..6828ea2 100644
> --- a/drivers/usb/gadget/function/u_ether.c
> +++ b/drivers/usb/gadget/function/u_ether.c
> @@ -48,6 +48,11 @@
>
>   #define UETH__VERSION	"29-May-2008"
>
> +/* Experiments show that both Linux and Windows hosts allow up to 16k
> + * frame sizes. Set the max size to 15k+52 to prevent allocating 32k
> + * blocks and still have efficient handling. */
> +#define GETHER_MAX_ETH_FRAME_LEN 15412
> +
>   struct eth_dev {
>   	/* lock is held while accessing port_usb
>   	 */
> @@ -146,7 +151,7 @@ static int ueth_change_mtu(struct net_device *net, int new_mtu)
>   	spin_lock_irqsave(&dev->lock, flags);
>   	if (dev->port_usb)
>   		status = -EBUSY;
> -	else if (new_mtu <= ETH_HLEN || new_mtu > ETH_FRAME_LEN)
> +	else if (new_mtu <= ETH_HLEN || new_mtu > GETHER_MAX_ETH_FRAME_LEN)
>   		status = -ERANGE;
>   	else
>   		net->mtu = new_mtu;
> @@ -294,7 +299,7 @@ static void rx_complete(struct usb_ep *ep, struct usb_request *req)
>   		while (skb2) {
>   			if (status < 0
>   					|| ETH_HLEN > skb2->len
> -					|| skb2->len > VLAN_ETH_FRAME_LEN) {
> +					|| skb2->len > GETHER_MAX_ETH_FRAME_LEN) {
>   				dev->net->stats.rx_errors++;
>   				dev->net->stats.rx_length_errors++;
>   				DBG(dev, "rx length %d\n", skb2->len);
>



Kind regards,

Mike Looijmans
System Expert

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