On Wed, 8 Feb 2017 15:41:20 -0800
Tom Herbert <t...@herbertland.com> wrote:
> +static inline int __xdp_run_one_hook(struct xdp_hook *hook,
> + struct xdp_buff *xdp)
> +{
> + void *priv = rcu_dereference(hook->priv);
> +
> + if (hook->is_bpf) {
> + /* Run BPF programs directly do avoid one layer of
> + * indirection.
> + */
> + return BPF_PROG_RUN((struct bpf_prog *)priv, (void *)xdp);
> + } else {
> + return hook->hookfn(priv, xdp);
> + }
> +}
> +
> +/* Core function to run the XDP hooks. This must be as fast as possible */
> +static inline int __xdp_hook_run(struct xdp_hook_set *hook_set,
> + struct xdp_buff *xdp,
> + struct xdp_hook **last_hook)
> +{
> + struct xdp_hook *hook;
> + int i, ret;
> +
> + if (unlikely(!hook_set))
> + return XDP_PASS;
> +
> + hook = &hook_set->hooks[0];
> + ret = __xdp_run_one_hook(hook, xdp);
> + *last_hook = hook;
> +
> + for (i = 1; i < hook_set->num; i++) {
> + if (ret != XDP_PASS)
> + break;
> + hook = &hook_set->hooks[i];
> + ret = __xdp_run_one_hook(hook, xdp);
> + }
> +
> + return ret;
> +}
There is one basic problem with this approach. There is no bulking and
no reuse of instruction cache. There is no revolution in this approach.
We will end-up with the same known performance problems when more hook
users get added.
Calling N-number of hooks per every packet, will just end-up flushing
the instruction cache (like the issues we have today).
Instead take N-packets, and then call the hooks by turn (store action
verdicts in packet-vector). Such an architecture would be inline with
that VPP, Snabb and DPDK is doing. Optimizing icache usage, and opens
up for smarter prefetching of lookup tables. Imagine, having hook-1
identify lookup bucket and start prefetch, hook-2 access the bucket and
prefetch table data, and hook-3 read data. This is what DPDK is doing
see[1], and VPP is doing similar tricks to get it to scale to large
route lookup tables.
[1] http://dpdk.org/doc/guides/prog_guide/packet_framework.html#figure-figure35
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
