On Sat, Oct 17, 2020 at 09:12:38AM +0200, sven.auha...@voleatech.de wrote:
> From: Sven Auhagen <sven.auha...@voleatech.de>
>
> Since we share the transmit queue with the slow path,
> it is possible that we run into a transmit queue timeout.
> This will reset the queue.
> This happens under high load when the fast path is using the
> transmit queue pretty much exclusively.
I'm kinda not leaning towards slow/fast path distinction here, IMHO it
would be better to state that transmit queues are shared between network
stack and XDP, but that's just a rant.
>
> By setting the transmit queues trans_start variable to jiffies
> in the two xdp xmit functions we avoid the timeout.
Probably a few more words of explanation would help here, specifically I
would say that netdev_start_xmit() sets trans_start to jiffies which is
later utilized by dev_watchdog(), so to avoid timeout, let stack know that
XDP xmit happened by bumping the trans_start within XDP Tx routines.
>
> Signed-off-by: Sven Auhagen <sven.auha...@voleatech.de>
> ---
> drivers/net/ethernet/intel/igb/igb_main.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c
> b/drivers/net/ethernet/intel/igb/igb_main.c
> index 55e708f75187..4a082c06f48d 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -2916,6 +2916,8 @@ static int igb_xdp_xmit_back(struct igb_adapter
> *adapter, struct xdp_buff *xdp)
>
> nq = txring_txq(tx_ring);
> __netif_tx_lock(nq, cpu);
> + /* Avoid transmit queue timeout since we share it with the slow path */
> + nq->trans_start = jiffies;
> ret = igb_xmit_xdp_ring(adapter, tx_ring, xdpf);
> __netif_tx_unlock(nq);
>
> @@ -2948,6 +2950,9 @@ static int igb_xdp_xmit(struct net_device *dev, int n,
> nq = txring_txq(tx_ring);
> __netif_tx_lock(nq, cpu);
>
> + /* Avoid transmit queue timeout since we share it with the slow path */
> + nq->trans_start = jiffies;
> +
> for (i = 0; i < n; i++) {
> struct xdp_frame *xdpf = frames[i];
> int err;
> --
> 2.20.1
>
