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pping: Add RTT-based sampling

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Add an option (-R, --rtt-rate) to adapt the rate sampling based on the
RTT of the flow. The sampling rate will be C * RTT, where C is a
configurable constant (ex 1.0 to get one sample every RTT), and RTT
is either the current minimum (default) or smoothed RTT of the
flow (chosen via the -t or --rtt-type option).

The smoothed RTT (sRTT) is updated for each calculated RTT, and is
calculated in a similar manner to srtt in the kernel's TCP stack. The
sRTT is a moving average of all RTTs, and is calculated according to
the formula:

  srtt = 7/8 * prev_srtt + 1/8 * rtt

To allow the user to pass a non-integer C (ex 0.1 to get 10 RTT
samples for every RTT-period), fixed-point arithmetic has been used
in the eBPF programs (due to lack of support for floats). The maximum
value for C has been limited to 10000 in order for it to be unlikely
that the C * RTT calculation will overflow (with C = 10000, overflow
will only occur if RTT > 28 seconds).

Signed-off-by: Simon Sundberg <simon.sundberg@kau.se>
This commit is contained in:
Simon Sundberg
2022-02-10 16:11:21 +01:00
parent c79c4e8571
commit 928a4144a9
3 changed files with 68 additions and 8 deletions
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32
pping/pping.c
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@@ -100,6 +100,8 @@ static const struct option long_options[] = {
{ "help", no_argument, NULL, 'h' },
{ "interface", required_argument, NULL, 'i' }, // Name of interface to run on
{ "rate-limit", required_argument, NULL, 'r' }, // Sampling rate-limit in ms
{ "rtt-rate", required_argument, NULL, 'R' }, // Sampling rate in terms of flow-RTT (ex 1 sample per RTT-interval)
{ "rtt-type", required_argument, NULL, 't' }, // What type of RTT the RTT-rate should be applied to ("min" or "smoothed"), only relevant if rtt-rate is provided
{ "force", no_argument, NULL, 'f' }, // Overwrite any existing XDP program on interface, remove qdisc on cleanup
{ "cleanup-interval", required_argument, NULL, 'c' }, // Map cleaning interval in s, 0 to disable
{ "format", required_argument, NULL, 'F' }, // Which format to output in (standard/json/ppviz)
@@ -167,14 +169,14 @@ static int parse_bounded_double(double *res, const char *str, double low,
static int parse_arguments(int argc, char *argv[], struct pping_config *config)
{
int err, opt;
double rate_limit_ms, cleanup_interval_s;
double rate_limit_ms, cleanup_interval_s, rtt_rate;
config->ifindex = 0;
config->force = false;
config->bpf_config.track_tcp = false;
config->bpf_config.track_icmp = false;
while ((opt = getopt_long(argc, argv, "hfTCi:r:c:F:I:", long_options,
while ((opt = getopt_long(argc, argv, "hfTCi:r:R:t:c:F:I:", long_options,
NULL)) != -1) {
switch (opt) {
case 'i':
@@ -203,6 +205,26 @@ static int parse_arguments(int argc, char *argv[], struct pping_config *config)
config->bpf_config.rate_limit =
rate_limit_ms * NS_PER_MS;
break;
case 'R':
err = parse_bounded_double(&rtt_rate, optarg, 0, 10000,
"rtt-rate");
if (err)
return -EINVAL;
config->bpf_config.rtt_rate =
DOUBLE_TO_FIXPOINT(rtt_rate);
break;
case 't':
if (strcmp(optarg, "min") == 0) {
config->bpf_config.use_srtt = false;
}
else if (strcmp(optarg, "smoothed") == 0) {
config->bpf_config.use_srtt = true;
} else {
fprintf(stderr,
"rtt-type must be \"min\" or \"smoothed\"\n");
return -EINVAL;
}
break;
case 'c':
err = parse_bounded_double(&cleanup_interval_s, optarg,
0, 7 * S_PER_DAY,
@@ -482,7 +504,7 @@ static bool flow_timeout(void *key_ptr, void *val_ptr, __u64 now)
if (print_event_func) {
fe.event_type = EVENT_TYPE_FLOW;
fe.timestamp = now;
memcpy(&fe.flow, key_ptr, sizeof(struct network_tuple));
fe.flow = *(struct network_tuple *)key_ptr;
fe.event_info.event = FLOW_EVENT_CLOSING;
fe.event_info.reason = EVENT_REASON_FLOW_TIMEOUT;
fe.source = EVENT_SOURCE_USERSPACE;
@@ -976,7 +998,9 @@ int main(int argc, char *argv[])
DECLARE_LIBBPF_OPTS(bpf_tc_opts, tc_egress_opts);
struct pping_config config = {
.bpf_config = { .rate_limit = 100 * NS_PER_MS },
.bpf_config = { .rate_limit = 100 * NS_PER_MS,
.rtt_rate = 0,
.use_srtt = false },
.cleanup_interval = 1 * NS_PER_SECOND,
.object_path = "pping_kern.o",
.ingress_prog = "pping_xdp_ingress",