Hi, It can be due to cpu C state. When the CPU is isolated, there is no task assigned to it when the pinned thread is not running thus increases the chance for it to go to deep sleep state, it is quite costly to wake up from deep sleep state. For non isolated cores, they are probably consistently running tasks thus lower chance to go to deep sleep state.
You can try to disable c state in bios and see if it helps. Best Regards, GS On Saturday, February 14, 2026 at 4:26:04 AM UTC+8 [email protected] wrote: No. Actually, after some retests my observation is that it happens regardless the thread is pinned or not. So, When thread *T* is pinned to CPU #10 and the task interval is set to 1ms, the average task execution time is *100 µs*. However, when the task interval is increased to 40ms on the same pinned core, the average execution time significantly degrades to *250 µs*. If T is not pinned, the result is same. piątek, 13 lutego 2026 o 18:39:03 UTC+1 Mark E. Dawson, Jr. napisał(a): Do you have a baseline for how your isolated core should perform using a tool like 'osnoise'? On Friday, February 13, 2026 at 10:18:49 AM UTC-6 [email protected] wrote: Hi, let's look at the example: The system is running with the following kernel parameters: isolcpus=10, nohz_full=10, nohz=on, idle=poll, intel_pstate=disable. We have a thread *T* that uses Thread.onSpinWait() while polling a lock-free shared queue. In this context, the *task interval* refers to the time elapsed between adding consecutive tasks to the queue. When thread *T* is pinned to CPU #10 and the task interval is set to 1ms, the average task execution time is *100 µs*. However, when the task interval is increased to 40ms on the same pinned core, the average execution time significantly degrades to *250 µs*. In contrast, when thread *T* is unpinned, the performance remains much more consistent. At a 1ms task interval, the average execution time is *110 µs*, and it only slightly increases to *120 µs* when the interval is extended to 40ms. -- You received this message because you are subscribed to the Google Groups "mechanical-sympathy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion, visit https://groups.google.com/d/msgid/mechanical-sympathy/0b6da827-4f52-40c9-a00d-43e067229f46n%40googlegroups.com.
