mirror of
https://github.com/kuhyx/testsAndMisc.git
synced 2026-11-11 14:07:49 +01:00
Krzysztof kuhy Rudnicki
836f4ef2de
Diagnosing "Steam downloads are slow" kept pointing at the ISP because every averaged measurement showed a steady ~170 Mbps. Sampling at 1s instead of 5s showed that plateau does not exist: the link alternates between ~450 Mbps bursts and multi-second stalls. Effective rate is burst x duty_cycle, and only the second factor was wrong. steam-download-duty.sh reports those two factors separately, which is what the Steam UI cannot do. line-speed-probe.sh separates burst from sustained throughput, because a single stream tops out near 180 Mbps on this line and reads convincingly as ISP shaping when it is not — a many-connection swarm reaches 986 Mbps with zero retransmits. Arithmetic is extracted into pure helpers with main() behind a BASH_SOURCE guard so the bats suite can source them without starting a measurement. install.sh installs bats and links both scripts onto PATH. Note: no CI workflow runs .sh/.bats tests, including the four shell tests that predate this one, so the suite is manual-only for now.
127 lines
4.5 KiB
Bash
Executable File
127 lines
4.5 KiB
Bash
Executable File
#!/bin/bash
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# ============================================================================
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# steam-download-duty.sh — measure a download's DUTY CYCLE, not its average.
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#
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# Why this exists: on this machine the link is not bandwidth-limited, but the
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# Steam client is. Sampling at 1 s shows Steam alternating between
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# multi-hundred-Mbps bursts and multi-second stalls in which it uses ~1% CPU,
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# no disk, and transmits only keepalives. Any averaged "Mbps" figure is really
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# burst_rate x duty_cycle
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# and hides which of the two factors is actually wrong.
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#
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# Measured 2026-07-19 (see the diagnosis writeup): Steam client 38% duty /
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# ~170 Mbps effective, vs depotdownloader -max-downloads 32 at 97% duty /
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# 696 Mbps effective on the same line, same CDN, same minute.
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#
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# Use this to compare download clients or regions objectively — the Steam UI's
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# averaged number cannot distinguish "slow link" from "idle client".
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#
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# Usage: steam-download-duty.sh [seconds] (default 60)
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# ============================================================================
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set -euo pipefail
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IFACE="${IFACE:-enp6s0}"
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IDLE_THRESHOLD_MBPS="${IDLE_THRESHOLD_MBPS:-20}" # below this = stalled second
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# --- pure helpers (unit-tested by linux_configuration/tests) ----------------
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# Convert a byte delta observed over N seconds into Mbps (integer).
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bytes_to_mbps() {
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local delta="$1" secs="$2"
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(( secs > 0 )) || { printf '0'; return; }
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printf '%d' $(( delta * 8 / secs / 1000000 ))
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}
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# Percentage of sampled seconds that carried traffic.
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duty_pct() {
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local active="$1" total="$2"
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(( total > 0 )) || { printf '0'; return; }
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printf '%d' $(( active * 100 / total ))
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}
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# Integer mean of the numeric arguments (0 when given none).
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mean_of() {
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(( $# > 0 )) || { printf '0'; return; }
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local sum=0 v
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for v in "$@"; do sum=$(( sum + v )); done
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printf '%d' $(( sum / $# ))
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}
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# Classify a run. Kept separate from printing so it can be asserted on.
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# LINK_LIMITED - transferring almost always; the rate is the rate
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# CLIENT_IDLE - fast when active but idle a lot => client's fault
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# MIXED - neither clean bursts nor high duty
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classify() {
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local duty="$1" burst="$2"
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if (( duty >= 80 )); then
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printf 'LINK_LIMITED'
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elif (( burst >= 400 )); then
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printf 'CLIENT_IDLE'
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else
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printf 'MIXED'
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fi
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}
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# --- measurement -----------------------------------------------------------
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rx_bytes() { cat "/sys/class/net/${IFACE}/statistics/rx_bytes"; }
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main() {
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local total="${1:-60}"
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local prev cur mbps active=0 peak=0
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local -a samples=() active_samples=() trace=()
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printf 'Sampling %ss at 1s resolution on %s ...\n\n' "$total" "$IFACE"
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prev=$(rx_bytes)
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local i
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for (( i = 1; i <= total; i++ )); do
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sleep 1
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cur=$(rx_bytes)
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mbps=$(bytes_to_mbps $(( cur - prev )) 1)
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prev=$cur
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samples+=("$mbps")
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if (( mbps > peak )); then peak=$mbps; fi
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if (( mbps >= IDLE_THRESHOLD_MBPS )); then
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active=$(( active + 1 )); active_samples+=("$mbps"); trace+=("#")
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else
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trace+=(".")
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fi
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done
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printf 'pattern (# = transferring, . = stalled):\n '
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printf '%s' "${trace[@]}"
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printf '\n\n'
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local duty burst overall
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duty=$(duty_pct "$active" "$total")
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burst=$(mean_of ${active_samples[@]+"${active_samples[@]}"})
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overall=$(mean_of ${samples[@]+"${samples[@]}"})
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printf 'duty cycle : %d%% (%ds transferring / %ds stalled)\n' \
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"$duty" "$active" "$(( total - active ))"
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printf 'rate when active: %d Mbps (peak %d)\n' "$burst" "$peak"
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printf 'effective avg : %d Mbps\n\n' "$overall"
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case "$(classify "$duty" "$burst")" in
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LINK_LIMITED)
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printf 'VERDICT: link is the limit — %d Mbps is close to what you get.\n' "$burst" ;;
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CLIENT_IDLE)
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printf 'VERDICT: NOT bandwidth-limited. Bursts reach %d Mbps but the\n' "$burst"
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printf ' transfer is idle %d%% of the time. At 100%% duty this\n' "$(( 100 - duty ))"
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printf ' link would give ~%d Mbps. Compare clients/regions by\n' "$burst"
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printf ' duty cycle, not by the averaged UI number.\n' ;;
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*)
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printf 'VERDICT: mixed — bursts only reach %d Mbps and duty is %d%%.\n' \
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"$burst" "$duty" ;;
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esac
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}
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# Only run when executed directly, so tests can source the helpers above.
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if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
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main "$@"
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fi
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