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net: mctp: usb: Allow multiple urbs in flight

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Currently, we stop tx queues when we have one urb submitted. This means
we will immediately hit dev_hard_start_xmit's tx-queues-off ->
NETDEV_TX_BUSY case, and revert to the requeue -> gso_skb single-dequeue
path, and no longer be able to pack skbs without an xmit_more
indication.

Instead, allow a few urbs to be in-flight, with a limit of 16kB of data
outstanding (after which we will disable queues). With this, the tx path
will cause fewer requeues (and therefore non-packed transfers) under
normal loads.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://patch.msgid.link/20260724-dev-mctp-usb-1-1-v5-12-e66bbba0dbdc@codeconstruct.com.au
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jeremy Kerr
2026-07-24 13:15:33 +08:00
committed by Jakub Kicinski
parent b4a27a474b
commit 88dbfe0d95
1 changed files with 29 additions and 4 deletions
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33
drivers/net/mctp/mctp-usb.c
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@@ -42,6 +42,9 @@ struct mctp_usb {
struct mctp_usblib_tx tx;
struct usb_anchor tx_anchor;
/* serialises tx_qmem updates to netdev queue states */
spinlock_t tx_qmem_lock;
int tx_qmem;
};
enum {
@@ -49,23 +52,41 @@ enum {
MCTP_USB_SUBCLASS_SPAN = 0x02,
};
/* We use a total-size limit for outstanding URBs, as the transfer counts
* may vary a lot between spanning- and non-spanning modes. In spanning mode,
* this will allow for a couple of max-sized transfers to be in flight. In
* non-spanning mode, 32.
*
* We want to avoid disabling the tx queue if possible; doing so will end up
* requeueing to gso_skb, and we only dequeue from that one skb at a time,
* so can no longer perform transfer packing.
*/
static const unsigned int TX_QMEM_MAX = 16384;
static void mctp_usb_out_complete(struct urb *urb)
{
struct mctp_usblib_tx_ctx *tx_ctx = urb->context;
struct mctp_usb *mctp_usb = mctp_usblib_tx_ctx_priv(tx_ctx);
unsigned int len = urb->transfer_buffer_length;
struct net_device *netdev = mctp_usb->netdev;
unsigned long flags;
mctp_usblib_tx_send_complete(tx_ctx, netdev, urb->status == 0);
usb_free_urb(urb);
netif_wake_queue(netdev);
spin_lock_irqsave(&mctp_usb->tx_qmem_lock, flags);
mctp_usb->tx_qmem -= len;
if (mctp_usb->tx_qmem < TX_QMEM_MAX && netif_running(netdev))
netif_wake_queue(netdev);
spin_unlock_irqrestore(&mctp_usb->tx_qmem_lock, flags);
}
static int mctp_usb_tx_send(struct mctp_usblib_tx_ctx *tx_ctx,
void *data, size_t len)
{
struct mctp_usb *mctp_usb = mctp_usblib_tx_ctx_priv(tx_ctx);
unsigned long flags;
struct urb *urb;
int rc;
@@ -80,8 +101,6 @@ static int mctp_usb_tx_send(struct mctp_usblib_tx_ctx *tx_ctx,
if (mctp_usb->span)
urb->transfer_flags |= URB_ZERO_PACKET;
netif_stop_queue(mctp_usb->netdev);
usb_anchor_urb(urb, &mctp_usb->tx_anchor);
rc = usb_submit_urb(urb, GFP_ATOMIC);
@@ -89,7 +108,12 @@ static int mctp_usb_tx_send(struct mctp_usblib_tx_ctx *tx_ctx,
netdev_dbg(mctp_usb->netdev, "TX urb submit failed, %d\n", rc);
usb_unanchor_urb(urb);
usb_free_urb(urb);
netif_start_queue(mctp_usb->netdev);
} else {
spin_lock_irqsave(&mctp_usb->tx_qmem_lock, flags);
mctp_usb->tx_qmem += len;
if (mctp_usb->tx_qmem >= TX_QMEM_MAX)
netif_stop_queue(mctp_usb->netdev);
spin_unlock_irqrestore(&mctp_usb->tx_qmem_lock, flags);
}
return rc;
@@ -353,6 +377,7 @@ static int mctp_usb_probe(struct usb_interface *intf,
spin_lock_init(&dev->rx_lock);
if (dev->span)
netdev->max_mtu = MCTP_USB_1_1_MTU_MAX;
spin_lock_init(&dev->tx_qmem_lock);
usb_set_intfdata(intf, dev);
rc = mctp_usblib_rx_init(&dev->rx, le16_to_cpu(ep_in->wMaxPacketSize),