Re: [PATCH bpf-next 05/10] ixgbe: xsk: terminate NAPI when XSK Rx queue gets full

Jesper Dangaard Brouer
2022-04-05T14:24:52Z

On 05/04/2022 13.06, Maciej Fijalkowski wrote:
> Correlate -ENOBUFS that was returned from xdp_do_redirect() with a XSK
> Rx queue being full. In such case, terminate the softirq processing and
> let the user space to consume descriptors from XSK Rx queue so that
> there is room that driver can use later on.
>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> ---
> .../ethernet/intel/ixgbe/ixgbe_txrx_common.h | 1 +
> drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 23 ++++++++++++-------
> 2 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_txrx_common.h b/drivers/net/ethernet/intel/ixgbe/ixgbe_txrx_common.h
> index bba3feaf3318..f1f69ce67420 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_txrx_common.h
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_txrx_common.h
> @@ -8,6 +8,7 @@
> #define IXGBE_XDP_CONSUMED BIT(0)
> #define IXGBE_XDP_TX BIT(1)
> #define IXGBE_XDP_REDIR BIT(2)
> +#define IXGBE_XDP_EXIT BIT(3)
>
> #define IXGBE_TXD_CMD (IXGBE_TXD_CMD_EOP | \
> IXGBE_TXD_CMD_RS)
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
> index dd7ff66d422f..475244a2c6e4 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
> @@ -109,9 +109,10 @@ static int ixgbe_run_xdp_zc(struct ixgbe_adapter *adapter,
>
> if (likely(act == XDP_REDIRECT)) {
> err = xdp_do_redirect(rx_ring->netdev, xdp, xdp_prog);
> - if (err)
> - goto out_failure;
> - return IXGBE_XDP_REDIR;
> + if (!err)
> + return IXGBE_XDP_REDIR;
> + result = (err == -ENOBUFS) ? IXGBE_XDP_EXIT : IXGBE_XDP_CONSUMED;
> + goto out_failure;
> }
>
> switch (act) {
> @@ -130,6 +131,9 @@ static int ixgbe_run_xdp_zc(struct ixgbe_adapter *adapter,
> if (result == IXGBE_XDP_CONSUMED)
> goto out_failure;
> break;
> + case XDP_DROP:
> + result = IXGBE_XDP_CONSUMED;
> + break;
> default:
> bpf_warn_invalid_xdp_action(rx_ring->netdev, xdp_prog, act);
> fallthrough;
> @@ -137,9 +141,6 @@ static int ixgbe_run_xdp_zc(struct ixgbe_adapter *adapter,
> out_failure:
> trace_xdp_exception(rx_ring->netdev, xdp_prog, act);
> fallthrough; /* handle aborts by dropping packet */
> - case XDP_DROP:
> - result = IXGBE_XDP_CONSUMED;
> - break;
> }
> return result;
> }
> @@ -304,10 +305,16 @@ int ixgbe_clean_rx_irq_zc(struct ixgbe_q_vector *q_vector,
> xdp_res = ixgbe_run_xdp_zc(adapter, rx_ring, bi->xdp);
>
> if (xdp_res) {
> - if (xdp_res & (IXGBE_XDP_TX | IXGBE_XDP_REDIR))
> + if (xdp_res == IXGBE_XDP_EXIT) {

Micro optimization note: Having this as the first if()-statement
defaults the compiler to think this is the likely() case. (But compilers
can obviously be smarter and can easily choose that the IXGBE_XDP_REDIR
branch is so simple that it takes it as the likely case).
Just wanted to mention this, given this is fash-path code.

> + failure = true;
> + xsk_buff_free(bi->xdp);
> + ixgbe_inc_ntc(rx_ring);
> + break;

I was wondering if we have a situation where we should set xdp_xmit bit
to trigger the call to xdp_do_flush_map later in function, but I assume
you have this covered.

> + } else if (xdp_res & (IXGBE_XDP_TX | IXGBE_XDP_REDIR)) {
> xdp_xmit |= xdp_res;
> - else
> + } else {
> xsk_buff_free(bi->xdp);
> + }
>
> bi->xdp = NULL;
> total_rx_packets++;