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Reduce the flow rate estimation frequency from 1 second to 1 ms.

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This reduces round-error issues and is generally more accurate -
at the expense of slightly higher CPU usage and a "more bouncy"
rate - that is, for a widely variable flow such as Netflix it
jumps around a lot more. I remain unconvinced that 1ms is the
right number - will continue to test.

Thanks again to Simon Sundberg for this suggestion.
This commit is contained in:
Herbert Wolverson committed 2024-02-29 11:05:37 -06:00
1 parent 7d6cbd417a
commit 23f2cfb9d8
1 file changed
+8 -5
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src/rust/lqos_sys/src/bpf/common/flows.h
+8 -5
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@@ -9,6 +9,7 @@
#define SECOND_IN_NANOS 1000000000
#define MS_IN_NANOS 1000000
//#define TIMESTAMP_INTERVAL_NANOS 10000000
// Some helpers to make understanding direction easier
@@ -88,7 +89,9 @@ static __always_inline struct flow_data_t new_flow_data(
.start_time = now,
.bytes_sent = { 0, 0 },
.packets_sent = { 0, 0 },
.next_count_time = { now + SECOND_IN_NANOS, now + SECOND_IN_NANOS },
// Track flow rates at an MS scale rather than per-second
// to minimize rounding errors.
.next_count_time = { now + MS_IN_NANOS, now + MS_IN_NANOS },
.last_count_time = { now, now },
.next_count_bytes = { dissector->skb_len, dissector->skb_len },
.rate_estimate_bps = { 0, 0 },
@@ -148,10 +151,10 @@ static __always_inline void update_flow_rates(
if (now > data->next_count_time[rate_index]) {
// Calculate the rate estimate
__u64 bits = (data->bytes_sent[rate_index] - data->next_count_bytes[rate_index])*8;
__u64 time = (now - data->last_count_time[rate_index]) / 1000000000; // Seconds
data->rate_estimate_bps[rate_index] = bits/time;
data->next_count_time[rate_index] = now + SECOND_IN_NANOS;
data->next_count_bytes[rate_index] = data->bytes_sent[0];
__u64 time = (now - data->last_count_time[rate_index]) / 1000000; // Milliseconds
data->rate_estimate_bps[rate_index] = (bits/time) * 1000; // bits per second
data->next_count_time[rate_index] = now + MS_IN_NANOS;
data->next_count_bytes[rate_index] = data->bytes_sent[rate_index];
data->last_count_time[rate_index] = now;
}
}