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--- linux [2025/10/25 14:23] – jotasandoku
+++ linux [2026/07/05 15:39] (current) – jotasandoku
@@ Line 1175: / Line 1175: @@
   load moduleethtool –i eth4 #
   ethtool -i eth4driver: sfcversion: 4.1.0.6734firmware-version: 3.3.0.6298bus-info: 0000:04:00.0 \\
+**TSHOOT IN KERNEL-BYPASS SYSTEMS**
+  cyclictest -p 99 -t 1 -a 3 -m -h 200 -D 60    # measures how late a thread actually wakes versus when it asked to
+  #   -p 99  real-time priority 99
+  #   -a 3   affine to CPU 3 (your isolated core)
+  #   -t 1   one thread
+  #   -h 200 build a latency histogram up to 200 us
+  #   -D 60  run for 60 seconds
+# structural tests before any ftracer
+  cat /proc/interrupts        # which IRQs are hitting CPU 3? (look at column 3)
+                              #   -> any device IRQ incrementing on your core = misrouted; fix affinity
+  cat /sys/devices/system/cpu/cpu3/cpuidle/state*/name   # which C-states are enabled?
+  cat /sys/devices/system/cpu/cpu3/cpufreq/scaling_governor  # 'performance'? or drifting?
+  grep . /sys/kernel/debug/tracing/... # (below)
+ ftrace # in-kernel tracer, extremely low overhead
+  trace-cmd record -p function_graph -M 8 sleep 60   # -M 8 = cpumask for core 3
+  trace-cmd report | less
+  # or watch what preempted your task:
+  trace-cmd record -e sched:sched_switch -e irq:irq_handler_entry -M 8 sleep 30
+----
 \\
 enabling spinning\\

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