net: cdc_ncm: set reasonable padding limits

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>

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index b9b562b9128a287d14d6d4466a83851cf4e0299b..9592d4669435c7bd0a957fb5762a7a982e901e74 100644 (file)
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -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)

diff --git a/include/linux/usb/cdc_ncm.h b/include/linux/usb/cdc_ncm.h
index 60a44b8a464eb68bc72bbf2672ea626a985a544d..79de6724d398023893073c4b7f6976728ad83638 100644 (file)
--- a/include/linux/usb/cdc_ncm.h
+++ b/include/linux/usb/cdc_ncm.h
@@ -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);