netdev - Re: [PATCH bpf-next 04/10] i40e: xsk: terminate NAPI when XSK Rx queue gets full

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Date:   Wed, 6 Apr 2022 18:04:58 +0200
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        magnus.karlsson@...el.com, bjorn@...nel.org, brouer@...hat.com,
        netdev@...r.kernel.org, maximmi@...dia.com,
        alexandr.lobakin@...el.com,
        Toke Hoiland Jorgensen <toke@...hat.com>
Subject: Re: [PATCH bpf-next 04/10] i40e: xsk: terminate NAPI when XSK Rx
 queue gets full

On Tue, Apr 05, 2022 at 03:04:17PM +0200, Jesper Dangaard Brouer wrote:
> 
> 
> 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@...el.com>
> > ---
> >   .../ethernet/intel/i40e/i40e_txrx_common.h    |  1 +
> >   drivers/net/ethernet/intel/i40e/i40e_xsk.c    | 21 ++++++++++++-------
> >   2 files changed, 15 insertions(+), 7 deletions(-)
> > 
> [...]
> 
> I noticed you are only doing this for the Zero-Copy variants.
> Wouldn't this also be a benefit for normal AF_XDP ?

Sorry for the delay, indeed this would improve AF_XDP in copy mode as
well, but only after a fix I have sent (not on lore yet :<).

I'll adjust patches to check for -ENOBUFS in $DRIVER_txrx.c and send a v2.

> 
> 
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > index c1d25b0b0ca2..9f9e4ce9a24d 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > @@ -161,9 +161,10 @@ static int i40e_run_xdp_zc(struct i40e_ring *rx_ring, struct xdp_buff *xdp)
> >   	if (likely(act == XDP_REDIRECT)) {
> >   		err = xdp_do_redirect(rx_ring->netdev, xdp, xdp_prog);
> > -		if (err)
> > -			goto out_failure;
> > -		return I40E_XDP_REDIR;
> > +		if (!err)
> > +			return I40E_XDP_REDIR;
> > +		result = (err == -ENOBUFS) ? I40E_XDP_EXIT : I40E_XDP_CONSUMED;
> > +		goto out_failure;
> >   	}
> >   	switch (act) {
> > @@ -175,6 +176,9 @@ static int i40e_run_xdp_zc(struct i40e_ring *rx_ring, struct xdp_buff *xdp)
> >   		if (result == I40E_XDP_CONSUMED)
> >   			goto out_failure;
> >   		break;
> > +	case XDP_DROP:
> > +		result = I40E_XDP_CONSUMED;
> > +		break;
> >   	default:
> >   		bpf_warn_invalid_xdp_action(rx_ring->netdev, xdp_prog, act);
> >   		fallthrough;
> > @@ -182,9 +186,6 @@ static int i40e_run_xdp_zc(struct i40e_ring *rx_ring, struct xdp_buff *xdp)
> >   out_failure:
> >   		trace_xdp_exception(rx_ring->netdev, xdp_prog, act);
> >   		fallthrough; /* handle aborts by dropping packet */
> > -	case XDP_DROP:
> > -		result = I40E_XDP_CONSUMED;
> > -		break;
> >   	}
> >   	return result;
> >   }
> > @@ -370,6 +371,12 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
> >   		xsk_buff_dma_sync_for_cpu(bi, rx_ring->xsk_pool);
> >   		xdp_res = i40e_run_xdp_zc(rx_ring, bi);
> > +		if (xdp_res == I40E_XDP_EXIT) {
> > +			failure = true;
> > +			xsk_buff_free(bi);
> > +			next_to_clean = (next_to_clean + 1) & count_mask;
> > +			break;
> > +		}
> >   		i40e_handle_xdp_result_zc(rx_ring, bi, rx_desc, &rx_packets,
> >   					  &rx_bytes, size, xdp_res);
> >   		total_rx_packets += rx_packets;
> > @@ -382,7 +389,7 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
> >   	cleaned_count = (next_to_clean - rx_ring->next_to_use - 1) & count_mask;
> >   	if (cleaned_count >= I40E_RX_BUFFER_WRITE)
> > -		failure = !i40e_alloc_rx_buffers_zc(rx_ring, cleaned_count);
> > +		failure |= !i40e_alloc_rx_buffers_zc(rx_ring, cleaned_count);
> >   	i40e_finalize_xdp_rx(rx_ring, xdp_xmit);
> >   	i40e_update_rx_stats(rx_ring, total_rx_bytes, total_rx_packets);
> > 
>