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samples/bpf: extend xdp_rxq_info to read packet payload 

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@redhat.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Jesper Dangaard Brouer 2018-06-25 16:27:43 +02:00 committed by Daniel Borkmann
parent a7f7547f5e
commit 0d25c43ab9
2 changed files with 47 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
samples/bpf/xdp_rxq_info_kern.c
View File

@ -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;
}

34
samples/bpf/xdp_rxq_info_user.c
View File

@ -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);
}
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;
}