On Fri, 29 Sep 2017 18:34:12 +0200, Jesper Dangaard Brouer wrote:
> The 'cpumap' is primary used as a backend map for XDP BPF helper
> call bpf_redirect_map() and XDP_REDIRECT action, like 'devmap'.
>
> This patch implement the main part of the map. It is not connected to
> the XDP redirect system yet, and no SKB allocation are done yet.
>
> The main concern in this patch is to ensure the datapath can run
> without any locking. This adds complexity to the setup and tear-down
> procedure, which assumptions are extra carefully documented in the
> code comments.
>
> V2: make sure array isn't larger than num possible CPUs
>
> Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com>
Few trivial nitpicks, hope you don't mind :)
> @@ -0,0 +1,555 @@
> +/* bpf/cpumap.c
> + *
> + * Copyright (c) 2017 Jesper Dangaard Brouer, Red Hat Inc.
> + * Released under terms in GPL version 2. See COPYING.
> + */
> +
> +/* The 'cpumap' is primary used as a backend map for XDP BPF helper
> + * call bpf_redirect_map() and XDP_REDIRECT action, like 'devmap'.
> + *
> + * Unlike devmap which redirect XDP frames out another NIC device,
> + * this map type redirect raw XDP frames to another CPU. The remote
> + * CPU will do SKB-allocation and call the normal network stack.
> + *
> + * This is a scalability and isolation mechanism, that allow
> + * separating the early driver network XDP layer, from the rest of the
> + * netstack, and assigning dedicated CPUs for this stage. This
> + * basically allows for 10G wirespeed pre-filtering via bpf.
> + */
> +#include <linux/bpf.h>
> +#include <linux/filter.h>
> +#include <linux/ptr_ring.h>
> +
> +#include <linux/sched.h>
> +#include <linux/workqueue.h>
> +#include <linux/kthread.h>
> +
> +/*
> + * General idea: XDP packets getting XDP redirected to another CPU,
> + * will maximum be stored/queued for one driver ->poll() call. It is
> + * guaranteed that setting flush bit and flush operation happen on
> + * same CPU. Thus, cpu_map_flush operation can deduct via this_cpu_ptr()
> + * which queue in bpf_cpu_map_entry contains packets.
> + */
> +
> +#define CPU_MAP_BULK_SIZE 8 /* 8 == one cacheline on 64-bit archs */
> +struct xdp_bulk_queue {
> + void *q[CPU_MAP_BULK_SIZE];
> + unsigned int count;
> +};
Out of curiosity - would it make sense to make sure the entire struct
fits into a cache line? The comment seems to indicate that the array is
sized to fit a cache line, but then there is also the count member...
> +/*
> + * After xchg pointer to bpf_cpu_map_entry, use the call_rcu() to
...
There is a mix for networking and non-networking style comments in this
file, is this intentional?
> +const struct bpf_map_ops cpu_map_ops = {
> + .map_alloc = cpu_map_alloc,
> + .map_free = cpu_map_free,
> + .map_delete_elem = cpu_map_delete_elem,
> + .map_update_elem = cpu_map_update_elem,
> + .map_lookup_elem = cpu_map_lookup_elem,
> + .map_get_next_key = cpu_map_get_next_key,
> +};
> +
> +
Extra new line.
> +/* Runs under RCU-read-side, plus in softirq under NAPI protection.
> + * Thus, safe percpu variable access.
> + */
> +static int bq_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_pkt
> *xdp_pkt)
> +{
> + struct xdp_bulk_queue *bq = this_cpu_ptr(rcpu->bulkq);
> +
> + if (unlikely(bq->count == CPU_MAP_BULK_SIZE)) {
> + bq_flush_to_queue(rcpu, bq);
> + }
Curly brackets not needed.
