LinkSettings.BurstWindow: size the token-bucket burst in line time - #8
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cskiraly wants to merge 1 commit into
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LinkSettings.BurstWindow: size the token-bucket burst in line time#8cskiraly wants to merge 1 commit into
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…line time Why: the token bucket accumulates at most one MTU, which is exact under a virtual clock but loses capacity on the real clock -- every timer wake-up overshoots its deadline slightly, and a bucket that cannot bank the overshoot forfeits it, so a 50 Mbps link delivers ~21 Mbps under load. What: LinkSettings.BurstWindow sets how much line time the bucket may accumulate. Zero keeps the current one-MTU behaviour (and stays the right setting under Go's testing/synctest virtual clock, where it is faithful); real-clock users set a few milliseconds to absorb scheduler overshoot. Measured on a calibration harness: a 50 Mbps link delivers 50 Mbps on the real clock with a 5 ms window.
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The token bucket accumulates at most one MTU, which is exact under a virtual clock but loses capacity on the real clock -- every timer wake-up overshoots its deadline slightly, and a bucket that cannot bank the overshoot forfeits it, so a 50 Mbps link delivers ~21 Mbps under load.
What changed: LinkSettings.BurstWindow sets how much line time the bucket may accumulate. Zero keeps the current one-MTU behaviour (and stays the right setting under Go's testing/synctest virtual clock, where it is faithful); real-clock users set a few milliseconds to absorb scheduler overshoot. Measured on a calibration harness: a 50 Mbps link delivers 50 Mbps on the real clock with a 5 ms window.