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feat: ServerScore replaced stdev with MAD

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zonyitoo
2024-07-28 14:54:24 +08:00
parent 009837484f
commit eea43c7cd6
2 changed files with 129 additions and 122 deletions
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34
crates/shadowsocks-service/src/local/loadbalancing/server_stat.rs
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@@ -33,6 +33,8 @@ pub struct ServerStatData {
pub latency_stdev: f64,
/// Score's average
pub latency_mean: f64,
/// Score's median absolute deviation
pub latency_mad: f64,
}
/// Statistic of a remote server
@@ -77,6 +79,7 @@ impl ServerStat {
fail_rate: 1.0,
latency_stdev: max_latency_stdev,
latency_mean: max_server_rtt as f64,
latency_mad: max_server_rtt as f64,
},
}
}
@@ -86,24 +89,27 @@ impl ServerStat {
let nrtt = self.data.latency_median as f64 / self.max_server_rtt as f64;
// Normalize stdev
let nstdev = self.data.latency_stdev / self.max_latency_stdev;
// let nstdev = self.data.latency_stdev / self.max_latency_stdev;
// Mormalize mad
let nmad = self.data.latency_mad / self.max_server_rtt as f64;
const SCORE_RTT_WEIGHT: f64 = 1.0;
const SCORE_FAIL_WEIGHT: f64 = 3.0;
const SCORE_STDEV_WEIGHT: f64 = 1.0;
// const SCORE_STDEV_WEIGHT: f64 = 0.0;
const SCORE_MAD_WEIGHT: f64 = 1.0;
// [EPSILON, 1]
// Just for avoiding divide by 0
let user_weight = self.user_weight.max(f32::EPSILON);
// Score = (norm_lat * 1.0 + prop_err * 3.0 + stdev * 1.0) / 5.0 / user_weight
// Score = (norm_lat * 1.0 + prop_err * 3.0 + (stdev || mad) * 1.0) / 5.0 / user_weight
//
// 1. The lower latency, the better
// 2. The lower errored count, the better
// 3. The lower latency's stdev, the better
// 3. The lower latency's stdev / mad, the better
// 4. The higher user's weight, the better
let score = (nrtt * SCORE_RTT_WEIGHT + self.data.fail_rate * SCORE_FAIL_WEIGHT + nstdev * SCORE_STDEV_WEIGHT)
/ (SCORE_RTT_WEIGHT + SCORE_FAIL_WEIGHT + SCORE_STDEV_WEIGHT)
let score = (nrtt * SCORE_RTT_WEIGHT + self.data.fail_rate * SCORE_FAIL_WEIGHT + nmad * SCORE_MAD_WEIGHT)
/ (SCORE_RTT_WEIGHT + SCORE_FAIL_WEIGHT + SCORE_MAD_WEIGHT)
/ user_weight as f64;
// Times 10000 converts to u32, for 0.0001 precision
@@ -146,6 +152,8 @@ impl ServerStat {
self.data.latency_stdev = self.max_latency_stdev;
self.data.latency_mean = self.max_server_rtt as f64;
self.data.latency_mad = self.max_server_rtt as f64;
if !vlat.is_empty() {
vlat.sort_unstable();
@@ -159,23 +167,33 @@ impl ServerStat {
};
if vlat.len() > 1 {
// STDEV
let n = vlat.len() as f64;
// mean
let mut total_lat = 0;
for s in &vlat {
total_lat += *s;
}
self.data.latency_mean = total_lat as f64 / n;
// STDEV
let mut acc_diff = 0.0;
for s in &vlat {
let diff = *s as f64 - self.data.latency_mean;
acc_diff += diff * diff;
}
// Corrected Sample Standard Deviation
self.data.latency_stdev = ((1.0 / (n - 1.0)) * acc_diff).sqrt();
self.data.latency_stdev = (acc_diff / (n - 1.0)).sqrt();
// MAD
let mut acc_abs_diff = 0.0;
for s in &vlat {
acc_abs_diff += (*s as f64 - self.data.latency_median as f64).abs();
}
self.data.latency_mad = acc_abs_diff / n;
} else {
self.data.latency_mean = vlat[0] as f64;
self.data.latency_mad = self.data.latency_mean; // mean = median in this case
}
}