Thread *T *is alway running - it has loops in manner:
while(!isInterrupted()) {
checkForWork();
noIdle
}
or
while(!isInterrupted()) {
checkForWork();
Thread.onSpinWait() // PAUSE on X86
}
In both cases I see this difference.
C-state should not be the case because of kernel option ilde=poll.
sobota, 14 lutego 2026 o 08:51:21 UTC+1 [email protected] napisał(a):
> 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.
>
>
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