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net: cdc_ncm: set reasonable padding limits

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We pad frames larger than X to maximum size for devices which
don't need a ZLP after maximum sized frames. This allows the
device to optimize its transfers for one fixed buffer size.

X was arbitrarily set at 512 bytes regardless of real buffer
maximum, causing extreme overheads due to excessive padding of
larger tx buffers. Limit the padding to at most 3 full USB
packets, still allowing the overhead to payload ratio of 3/1.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Bjørn Mork 2014-05-16 21:48:24 +02:00 committed by David S. Miller
parent 70559b8970
commit 43e4c6dfc0
2 changed files with 7 additions and 2 deletions
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8
drivers/net/usb/cdc_ncm.c
View file

@ -213,6 +213,10 @@ static void cdc_ncm_update_rxtx_max(struct usbnet *dev, u32 new_rx, u32 new_tx)
/* max qlen depend on hard_mtu and rx_urb_size */
usbnet_update_max_qlen(dev);
/* never pad more than 3 full USB packets per transfer */
ctx->min_tx_pkt = clamp_t(u16, ctx->tx_max - 3 * usb_maxpacket(dev->udev, dev->out, 1),
CDC_NCM_MIN_TX_PKT, ctx->tx_max);
}
/* helpers for NCM and MBIM differences */
@ -947,7 +951,7 @@ cdc_ncm_fill_tx_frame(struct usbnet *dev, struct sk_buff *skb, __le32 sign)
/* variables will be reset at next call */
}
/* If collected data size is less or equal CDC_NCM_MIN_TX_PKT
/* If collected data size is less or equal ctx->min_tx_pkt
* bytes, we send buffers as it is. If we get more data, it
* would be more efficient for USB HS mobile device with DMA
* engine to receive a full size NTB, than canceling DMA
@ -957,7 +961,7 @@ cdc_ncm_fill_tx_frame(struct usbnet *dev, struct sk_buff *skb, __le32 sign)
* a ZLP after full sized NTBs.
*/
if (!(dev->driver_info->flags & FLAG_SEND_ZLP) &&
skb_out->len > CDC_NCM_MIN_TX_PKT)
skb_out->len > ctx->min_tx_pkt)
memset(skb_put(skb_out, ctx->tx_max - skb_out->len), 0,
ctx->tx_max - skb_out->len);
else if (skb_out->len < ctx->tx_max && (skb_out->len % dev->maxpacket) == 0)

1
include/linux/usb/cdc_ncm.h
View file

@ -115,6 +115,7 @@ struct cdc_ncm_ctx {
u16 tx_seq;
u16 rx_seq;
u16 connected;
u16 min_tx_pkt;
};
u8 cdc_ncm_select_altsetting(struct usb_interface *intf);