On Thu, Oct 10, 2019 at 1:12 AM Magnus Karlsson
<magnus.karlsson@xxxxxxxxx> wrote:
>
> Added sections on all the bind flags, libbpf, all the setsockopts and
> all the getsockopts. Also updated the document to reflect the latest
> features and to correct some spelling errors.
>
> Signed-off-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
thanks for the update. Overall looks good.
Few nits below:
> +What socket will then a packet arrive on? This is decided by the XDP
> +program. Put all the sockets in the XSK_MAP and just indicate which
> +index in the array you would like to send each packet to. A simple
> +round-robin example of distributing packets is shown below:
> +
> +.. code-block:: c
> +
> + #define KBUILD_MODNAME "af_xdp_example"
what is this for?
It's not a kernel module.
> + #include <uapi/linux/bpf.h>
why 'uapi' ? It should use only user space headers.
> + #include "bpf_helpers.h"
> +
> + #define MAX_SOCKS 16
> +
> + struct bpf_map_def SEC("maps") xsks_map = {
> + .type = BPF_MAP_TYPE_XSKMAP,
> + .key_size = sizeof(int),
> + .value_size = sizeof(int),
> + .max_entries = MAX_SOCKS,
> + };
Could you switch to BTF defined maps?
libbpf will forever support old style as well,
but documentation should point to the latest.
> +
> + struct bpf_map_def SEC("maps") rr_map = {
> + .type = BPF_MAP_TYPE_PERCPU_ARRAY,
> + .key_size = sizeof(int),
> + .value_size = sizeof(unsigned int),
> + .max_entries = 1,
> + };
> +
> + SEC("xdp_sock") int xdp_sock_prog(struct xdp_md *ctx)
> + {
> + int key = 0, idx;
> + unsigned int *rr;
> +
> + rr = bpf_map_lookup_elem(&rr_map, &key);
> + if (!rr)
> + return XDP_ABORTED;
> +
> + *rr = (*rr + 1) & (MAX_SOCKS - 1);
> + idx = *rr;
> +
> + return bpf_redirect_map(&xsks_map, idx, 0);
> + }
> +
> + char _license[] SEC("license") = "GPL";
Above sample doesn't use gpl-only helpers. Why add above line?
> +.. code-block:: c
> +
> + if (xsk_ring_prod__needs_wakeup(&my_tx_ring))
> + sendto(xsk_socket__fd(xsk_handle), NULL, 0, MSG_DONTWAIT, NULL, 0);
> +
> +I.e., only use the syscall if the flag is set.
> +
> +We recommend that you always enable this mode as it can lead to
> +magnitudes better performance if you run the application and the
> +driver on the same core and somewhat better performance even if you
> +use different cores for the application and the kernel driver, as it
> +reduces the number of syscalls needed for the TX path.
"magnitudes better performance"? Is it really at least 20 times better?
> -Naive ring dequeue and enqueue could look like this::
> +Naive ring dequeue and enqueue could look like this:
lol. That's a good typo.
