netdev - Re: [PATCH bpf-next 4/6] bpf: cpumap: add the possibility to attach an eBPF program to cpumap

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Date:   Mon, 1 Jun 2020 15:36:18 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, davem@...emloft.net,
        ast@...nel.org, brouer@...hat.com, toke@...hat.com,
        daniel@...earbox.net, lorenzo.bianconi@...hat.com,
        dsahern@...nel.org
Subject: Re: [PATCH bpf-next 4/6] bpf: cpumap: add the possibility to attach
 an eBPF program to cpumap

On Sun, May 31, 2020 at 11:46:49PM +0200, Lorenzo Bianconi wrote:
> +
> +		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;
> +			int err;
>  
>  			/* 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;
> +			}

I'm not sure compiler will be smart enough to hoist !prog check out of the loop.
Otherwise default cpumap case will be a bit slower.
I'd like to see performance numbers before/after and acks from folks
who are using cpumap before applying.
Also please add selftest for it. samples/bpf/ in patch 6 is not enough.

Other than the above the feature looks good to me. It nicely complements devmap.