tuner: let the CPU test settle before judging stability

Pinning the governor was not enough: the monitor thread starts sampling at t=0,
before sysbench has spun every thread up, so it caught the machine still idling
and that one low reading became the "minimum under load". The control proves it
— a known-good 3500 MHz was rejected at "1396 MHz" while the live frequency
mid-bench was 3493.

It now ignores the first 8 seconds. With that, the ladder runs clean on this
board: 3500/3600/3700/3800/3900/4000 all pass, scores climbing 5118 -> 5849
ev/s (+14%), and 4000 holds 3971 MHz at 81 C.

Worth knowing: 4000 is crash-free over a 6-minute CPU+GPU soak (0 MCEs) but the
board then throttles to ~3400 MHz pinned at 86 C — past that point the limit is
the heatsink, not the silicon.

Author: MTSistemi

apps/tuner/skillfish-tuner-helper

@@ -314,6 +314,13 @@ def bench_cpu(secs=60):
     samp={"minf":99999,"maxt":0}
     stop=threading.Event()
     def mon():
+        # sysbench needs a moment to spin every thread up. Sampling from t=0 caught
+        # the machine still idling and that single low reading became the "minimum",
+        # failing even a known-good clock — 3500 was rejected at 1396 MHz while the
+        # live frequency mid-bench was 3493. Let the load settle before believing it.
+        deadline = time.monotonic() + 8
+        while not stop.is_set() and time.monotonic() < deadline:
+            time.sleep(0.5)
         while not stop.is_set():
             f=cpu_min_freq();  t=temp("k10temp")
             if f>0 and f<samp["minf"]: samp["minf"]=f

system/usr/local/bin/skillfish-tuner-helper

@@ -314,6 +314,13 @@ def bench_cpu(secs=60):
     samp={"minf":99999,"maxt":0}
     stop=threading.Event()
     def mon():
+        # sysbench needs a moment to spin every thread up. Sampling from t=0 caught
+        # the machine still idling and that single low reading became the "minimum",
+        # failing even a known-good clock — 3500 was rejected at 1396 MHz while the
+        # live frequency mid-bench was 3493. Let the load settle before believing it.
+        deadline = time.monotonic() + 8
+        while not stop.is_set() and time.monotonic() < deadline:
+            time.sleep(0.5)
         while not stop.is_set():
             f=cpu_min_freq();  t=temp("k10temp")
             if f>0 and f<samp["minf"]: samp["minf"]=f