Subject: Re: [PATCH v2 bpf-next 4/8] bpf: cpumap: add the possibility to attach an eBPF program to cpumap

From: Jesper Dangaard Brouer <[email-masked]>
Date: Mon, 22 Jun 2020 11:48:37 +0200

On Sat, 20 Jun 2020 00:57:20 +0200
Lorenzo Bianconi <[email-masked]> wrote:

> +static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
> +				    void **xdp_frames, int n,
> +				    struct xdp_cpumap_stats *stats)
> +{
> +	struct xdp_rxq_info rxq;

I do think we can merge this code as-is (and I actually re-factored this
code offlist), but I have some optimizations I would like to try out.

E.g. as I've tried to explain over IRC, it will be possible to avoid
having to reconstruct xdp_rxq_info here, as we can use the
expected_attach_type and remap the BPF instructions to use info from
xdp_frame.  I want to benchmark it first, to see if it is worth it (we
will only save 2 store operations in a likely cache-hot area).

> +	struct bpf_prog *prog;
> +	struct xdp_buff xdp;
> +	int i, nframes = 0;
> +
> +	if (!rcpu->prog)
> +		return n;
> +
> +	xdp_set_return_frame_no_direct();
> +	xdp.rxq = &rxq;
> +
> +	rcu_read_lock();
> +
> +	prog = READ_ONCE(rcpu->prog);
> +	for (i = 0; i < n; i++) {
> +		struct xdp_frame *xdpf = xdp_frames[i];
> +		u32 act;
> +		int err;
> +
> +		rxq.dev = xdpf->dev_rx;
> +		rxq.mem = xdpf->mem;
> +		/* TODO: report queue_index to xdp_rxq_info */
> +
> +		xdp_convert_frame_to_buff(xdpf, &xdp);
> +
> +		act = bpf_prog_run_xdp(prog, &xdp);
> +		switch (act) {
> +		case XDP_PASS:
> +			err = xdp_update_frame_from_buff(&xdp, xdpf);
> +			if (err < 0) {
> +				xdp_return_frame(xdpf);
> +				stats->drop++;
> +			} else {
> +				xdp_frames[nframes++] = xdpf;
> +				stats->pass++;
> +			}
> +			break;
> +		default:
> +			bpf_warn_invalid_xdp_action(act);
> +			/* fallthrough */
> +		case XDP_DROP:
> +			xdp_return_frame(xdpf);
> +			stats->drop++;
> +			break;
> +		}
> +	}
> +
> +	rcu_read_unlock();
> +	xdp_clear_return_frame_no_direct();
> +
> +	return nframes;
> +}

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer