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Date: Tue, 26 Jun 2018 16:53:15 -0700
From: Song Liu <liu.song.a23@...il.com>
To: Jesper Dangaard Brouer <brouer@...hat.com>
Cc: Networking <netdev@...r.kernel.org>,
Daniel Borkmann <borkmann@...earbox.net>,
Toke Høiland-Jørgensen <toke@...e.dk>,
Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [bpf-next PATCH 1/2] samples/bpf: extend xdp_rxq_info to read
packet payload
On Mon, Jun 25, 2018 at 7:27 AM, Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
> There is a cost associated with reading the packet data payload
> that this test ignored. Add option --read to allow enabling
> reading part of the payload.
>
> This sample/tool helps us analyse an issue observed with a NIC
> mlx5 (ConnectX-5 Ex) and an Intel(R) Xeon(R) CPU E5-1650 v4.
>
> With no_touch of data:
>
> Running XDP on dev:mlx5p1 (ifindex:8) action:XDP_DROP options:no_touch
> XDP stats CPU pps issue-pps
> XDP-RX CPU 0 14,465,157 0
> XDP-RX CPU 1 14,464,728 0
> XDP-RX CPU 2 14,465,283 0
> XDP-RX CPU 3 14,465,282 0
> XDP-RX CPU 4 14,464,159 0
> XDP-RX CPU 5 14,465,379 0
> XDP-RX CPU total 86,789,992
>
> When not touching data, we observe that the CPUs have idle cycles.
> When reading data the CPUs are 100% busy in softirq.
>
> With reading data:
>
> Running XDP on dev:mlx5p1 (ifindex:8) action:XDP_DROP options:read
> XDP stats CPU pps issue-pps
> XDP-RX CPU 0 9,620,639 0
> XDP-RX CPU 1 9,489,843 0
> XDP-RX CPU 2 9,407,854 0
> XDP-RX CPU 3 9,422,289 0
> XDP-RX CPU 4 9,321,959 0
> XDP-RX CPU 5 9,395,242 0
> XDP-RX CPU total 56,657,828
>
> The effect seen above is a result of cache-misses occuring when
> more RXQs are being used. Based on perf-event observations, our
> conclusion is that the CPUs DDIO (Direct Data I/O) choose to
> deliver packet into main memory, instead of L3-cache. We also
> found, that this can be mitigated by either using less RXQs or by
> reducing NICs the RX-ring size.
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...e.dk>
> ---
> samples/bpf/xdp_rxq_info_kern.c | 19 +++++++++++++++++++
> samples/bpf/xdp_rxq_info_user.c | 34 ++++++++++++++++++++++++++++------
> 2 files changed, 47 insertions(+), 6 deletions(-)
>
> diff --git a/samples/bpf/xdp_rxq_info_kern.c b/samples/bpf/xdp_rxq_info_kern.c
> index 3fd209291653..61af6210df2f 100644
> --- a/samples/bpf/xdp_rxq_info_kern.c
> +++ b/samples/bpf/xdp_rxq_info_kern.c
> @@ -4,6 +4,8 @@
> * Example howto extract XDP RX-queue info
> */
> #include <uapi/linux/bpf.h>
> +#include <uapi/linux/if_ether.h>
> +#include <uapi/linux/in.h>
> #include "bpf_helpers.h"
>
> /* Config setup from with userspace
> @@ -14,6 +16,11 @@
> struct config {
> __u32 action;
> int ifindex;
> + __u32 options;
> +};
> +enum cfg_options_flags {
> + NO_TOUCH = 0x0U,
> + READ_MEM = 0x1U,
> };
> struct bpf_map_def SEC("maps") config_map = {
> .type = BPF_MAP_TYPE_ARRAY,
> @@ -90,6 +97,18 @@ int xdp_prognum0(struct xdp_md *ctx)
> if (key == MAX_RXQs)
> rxq_rec->issue++;
>
> + /* Default: Don't touch packet data, only count packets */
> + if (unlikely(config->options & READ_MEM)) {
> + struct ethhdr *eth = data;
> +
> + if (eth + 1 > data_end)
> + return XDP_ABORTED;
> +
> + /* Avoid compiler removing this: Drop non 802.3 Ethertypes */
> + if (ntohs(eth->h_proto) < ETH_P_802_3_MIN)
> + return XDP_ABORTED;
> + }
> +
> return config->action;
> }
>
> diff --git a/samples/bpf/xdp_rxq_info_user.c b/samples/bpf/xdp_rxq_info_user.c
> index e4e9ba52bff0..435485d4f49e 100644
> --- a/samples/bpf/xdp_rxq_info_user.c
> +++ b/samples/bpf/xdp_rxq_info_user.c
> @@ -50,6 +50,7 @@ static const struct option long_options[] = {
> {"sec", required_argument, NULL, 's' },
> {"no-separators", no_argument, NULL, 'z' },
> {"action", required_argument, NULL, 'a' },
> + {"readmem", no_argument, NULL, 'r' },
> {0, 0, NULL, 0 }
> };
>
> @@ -66,6 +67,11 @@ static void int_exit(int sig)
> struct config {
> __u32 action;
> int ifindex;
> + __u32 options;
> +};
> +enum cfg_options_flags {
> + NO_TOUCH = 0x0U,
> + READ_MEM = 0x1U,
> };
> #define XDP_ACTION_MAX (XDP_TX + 1)
> #define XDP_ACTION_MAX_STRLEN 11
> @@ -109,6 +115,16 @@ static void list_xdp_actions(void)
> printf("\n");
> }
>
> +static char* options2str(enum cfg_options_flags flag)
> +{
> + if (flag == NO_TOUCH)
> + return "no_touch";
> + if (flag & READ_MEM)
> + return "read";
> + fprintf(stderr, "ERR: Unknown config option flags");
> + exit(EXIT_FAIL);
> +}
> +
enum cfg_options_flags is used as a bitmap in other parts of the sample.
So this function is a little weird (with more flags added).
Thanks,
Song
> static void usage(char *argv[])
> {
> int i;
> @@ -305,7 +321,7 @@ static __u64 calc_errs_pps(struct datarec *r,
>
> static void stats_print(struct stats_record *stats_rec,
> struct stats_record *stats_prev,
> - int action)
> + int action, __u32 cfg_opt)
> {
> unsigned int nr_rxqs = bpf_map__def(rx_queue_index_map)->max_entries;
> unsigned int nr_cpus = bpf_num_possible_cpus();
> @@ -316,8 +332,8 @@ static void stats_print(struct stats_record *stats_rec,
> int i;
>
> /* Header */
> - printf("\nRunning XDP on dev:%s (ifindex:%d) action:%s\n",
> - ifname, ifindex, action2str(action));
> + printf("\nRunning XDP on dev:%s (ifindex:%d) action:%s options:%s\n",
> + ifname, ifindex, action2str(action), options2str(cfg_opt));
>
> /* stats_global_map */
> {
> @@ -399,7 +415,7 @@ static inline void swap(struct stats_record **a, struct stats_record **b)
> *b = tmp;
> }
>
> -static void stats_poll(int interval, int action)
> +static void stats_poll(int interval, int action, __u32 cfg_opt)
> {
> struct stats_record *record, *prev;
>
> @@ -410,7 +426,7 @@ static void stats_poll(int interval, int action)
> while (1) {
> swap(&prev, &record);
> stats_collect(record);
> - stats_print(record, prev, action);
> + stats_print(record, prev, action, cfg_opt);
> sleep(interval);
> }
>
> @@ -421,6 +437,7 @@ static void stats_poll(int interval, int action)
>
> int main(int argc, char **argv)
> {
> + __u32 cfg_options= NO_TOUCH ; /* Default: Don't touch packet memory */
> struct rlimit r = {10 * 1024 * 1024, RLIM_INFINITY};
> struct bpf_prog_load_attr prog_load_attr = {
> .prog_type = BPF_PROG_TYPE_XDP,
> @@ -435,6 +452,7 @@ int main(int argc, char **argv)
> int interval = 2;
> __u32 key = 0;
>
> +
> char action_str_buf[XDP_ACTION_MAX_STRLEN + 1 /* for \0 */] = { 0 };
> int action = XDP_PASS; /* Default action */
> char *action_str = NULL;
> @@ -496,6 +514,9 @@ int main(int argc, char **argv)
> action_str = (char *)&action_str_buf;
> strncpy(action_str, optarg, XDP_ACTION_MAX_STRLEN);
> break;
> + case 'r':
> + cfg_options |= READ_MEM;
> + break;
> case 'h':
> error:
> default:
> @@ -522,6 +543,7 @@ int main(int argc, char **argv)
> }
> }
> cfg.action = action;
> + cfg.options = cfg_options;
>
> /* Trick to pretty printf with thousands separators use %' */
> if (use_separators)
> @@ -542,6 +564,6 @@ int main(int argc, char **argv)
> return EXIT_FAIL_XDP;
> }
>
> - stats_poll(interval, action);
> + stats_poll(interval, action, cfg_options);
> return EXIT_OK;
> }
>
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