netdev - Re: [RFC bpf-next 1/2] bpf: cpumap: add the possibility to attach a eBPF program to cpumap

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Date:   Fri, 22 May 2020 11:44:04 -0600
From:   David Ahern <dsahern@...il.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     ast@...nel.org, davem@...emloft.net, brouer@...hat.com,
        daniel@...earbox.net, lorenzo.bianconi@...hat.com,
        dsahern@...nel.org
Subject: Re: [RFC bpf-next 1/2] bpf: cpumap: add the possibility to attach a
 eBPF program to cpumap

On 5/22/20 10:11 AM, Lorenzo Bianconi wrote:
> @@ -259,28 +270,64 @@ static int cpu_map_kthread_run(void *data)
>  		 * kthread CPU pinned. Lockless access to ptr_ring
>  		 * consume side valid as no-resize allowed of queue.
>  		 */
> -		n = ptr_ring_consume_batched(rcpu->queue, frames, CPUMAP_BATCH);
> +		n = ptr_ring_consume_batched(rcpu->queue, xdp_frames,
> +					     CPUMAP_BATCH);
>  
> +		rcu_read_lock();
> +
> +		prog = READ_ONCE(rcpu->prog);
>  		for (i = 0; i < n; i++) {
> -			void *f = frames[i];
> +			void *f = xdp_frames[i];
>  			struct page *page = virt_to_page(f);
> +			struct xdp_frame *xdpf;
> +			struct xdp_buff xdp;
> +			u32 act;
>  
>  			/* Bring struct page memory area to curr CPU. Read by
>  			 * build_skb_around via page_is_pfmemalloc(), and when
>  			 * freed written by page_frag_free call.
>  			 */
>  			prefetchw(page);
> +			if (!prog) {
> +				frames[nframes++] = xdp_frames[i];
> +				continue;
> +			}
> +
> +			xdpf = f;
> +			xdp.data_hard_start = xdpf->data - xdpf->headroom;
> +			xdp.data = xdpf->data;
> +			xdp.data_end = xdpf->data + xdpf->len;
> +			xdp.data_meta = xdpf->data - xdpf->metasize;
> +			xdp.frame_sz = xdpf->frame_sz;
> +			/* TODO: rxq */
> +
> +			act = bpf_prog_run_xdp(prog, &xdp);

Why not run the program in cpu_map_enqueue before converting from
xdp_buff to xdp_frame?