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xmrig-auto-pause: add hysteresis to prevent stop/start thrashing

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xmrig's RandomX pollutes the L3 cache, making other processes appear
~3-8% busier. With a single 5% threshold for both stopping and
resuming, the script oscillates: start xmrig -> cache pressure
inflates CPU -> stop xmrig -> CPU drops -> restart -> repeat.

Split into CPU_STOP_THRESHOLD (15%) and CPU_RESUME_THRESHOLD (5%).
The stop threshold sits above xmrig's indirect pressure, so only
genuine workloads trigger a pause. The resume threshold confirms the
system is truly idle before restarting.
This commit is contained in:
Simon Gardling
2026-04-06 20:33:58 -04:00
parent 738861fd53
commit d48f27701f
3 changed files with 38 additions and 15 deletions
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13
tests/xmrig-auto-pause.nix
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@@ -39,13 +39,15 @@ pkgs.testers.runNixOSTest {
# POLL_INTERVAL=1 keeps detection latency low.
# GRACE_PERIOD=5 is long enough to verify "stays stopped" but short
# enough that the full test completes in reasonable time.
# CPU_THRESHOLD=10 catches a single busy-loop on a 1-2 core VM.
# CPU_STOP_THRESHOLD=20 catches a busy-loop on a 1-2 core VM (50-100%)
# without triggering from normal VM noise.
# CPU_RESUME_THRESHOLD=10 is the idle cutoff for a 1-2 core VM.
POLL_INTERVAL = "1"
GRACE_PERIOD = "5"
CPU_THRESHOLD = "10"
CPU_STOP_THRESHOLD = "20"
CPU_RESUME_THRESHOLD = "10"
STARTUP_COOLDOWN = "4"
STATE_DIR = "/tmp/xap-state"
def start_cpu_load(name):
"""Start a non-nice CPU burn as a transient systemd unit."""
machine.succeed(
@@ -62,13 +64,16 @@ pkgs.testers.runNixOSTest {
f"systemd-run --unit={unit_name} "
f"--setenv=POLL_INTERVAL={POLL_INTERVAL} "
f"--setenv=GRACE_PERIOD={GRACE_PERIOD} "
f"--setenv=CPU_THRESHOLD={CPU_THRESHOLD} "
f"--setenv=CPU_STOP_THRESHOLD={CPU_STOP_THRESHOLD} "
f"--setenv=CPU_RESUME_THRESHOLD={CPU_RESUME_THRESHOLD} "
f"--setenv=STARTUP_COOLDOWN={STARTUP_COOLDOWN} "
f"--setenv=STATE_DIR={STATE_DIR} "
f"{PYTHON} {SCRIPT}"
)
# Monitor needs two consecutive polls to compute a CPU delta.
time.sleep(3)
# Monitor needs two consecutive polls to compute a CPU delta.
time.sleep(3)
start_all()
machine.wait_for_unit("multi-user.target")