Re: [PATCH v2 bpf-next] cpumap: bulk skb using netif_receive_skb_list

Daniel Borkmann
2021-04-15T15:07:03Z

On 4/13/21 6:22 PM, Lorenzo Bianconi wrote:
> Rely on netif_receive_skb_list routine to send skbs converted from
> xdp_frames in cpu_map_kthread_run in order to improve i-cache usage.
> The proposed patch has been tested running xdp_redirect_cpu bpf sample
> available in the kernel tree that is used to redirect UDP frames from
> ixgbe driver to a cpumap entry and then to the networking stack.
> UDP frames are generated using pkt_gen.
>
> $xdp_redirect_cpu --cpu <cpu> --progname xdp_cpu_map0 --dev <eth>
>
> bpf-next: ~2.2Mpps
> bpf-next + cpumap skb-list: ~3.15Mpps
>
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> ---
> Changes since v1:
> - fixed comment
> - rebased on top of bpf-next tree
> ---
> kernel/bpf/cpumap.c | 11 +++++------
> 1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> index 0cf2791d5099..d89551a508b2 100644
> --- a/kernel/bpf/cpumap.c
> +++ b/kernel/bpf/cpumap.c
> @@ -27,7 +27,7 @@
> #include <linux/capability.h>
> #include <trace/events/xdp.h>
>
> -#include <linux/netdevice.h> /* netif_receive_skb_core */
> +#include <linux/netdevice.h> /* netif_receive_skb_list */
> #include <linux/etherdevice.h> /* eth_type_trans */
>
> /* General idea: XDP packets getting XDP redirected to another CPU,
> @@ -257,6 +257,7 @@ static int cpu_map_kthread_run(void *data)
> void *frames[CPUMAP_BATCH];
> void *skbs[CPUMAP_BATCH];
> int i, n, m, nframes;
> + LIST_HEAD(list);
>
> /* Release CPU reschedule checks */
> if (__ptr_ring_empty(rcpu->queue)) {
> @@ -305,7 +306,6 @@ static int cpu_map_kthread_run(void *data)
> for (i = 0; i < nframes; i++) {
> struct xdp_frame *xdpf = frames[i];
> struct sk_buff *skb = skbs[i];
> - int ret;
>
> skb = __xdp_build_skb_from_frame(xdpf, skb,
> xdpf->dev_rx);
> @@ -314,11 +314,10 @@ static int cpu_map_kthread_run(void *data)
> continue;
> }
>
> - /* Inject into network stack */
> - ret = netif_receive_skb_core(skb);
> - if (ret == NET_RX_DROP)
> - drops++;
> + list_add_tail(&skb->list, &list);
> }
> + netif_receive_skb_list(&list);
> +
> /* Feedback loop via tracepoint */
> trace_xdp_cpumap_kthread(rcpu->map_id, n, drops, sched, &stats);

Given we stop counting drops with the netif_receive_skb_list(), we should then
also remove drops from trace_xdp_cpumap_kthread(), imho, as otherwise it is rather
misleading (as in: drops actually happening, but 0 are shown from the tracepoint).
Given they are not considered stable API, I would just remove those to make it clear
to users that they cannot rely on this counter anymore anyway.

Thanks,
Daniel