Cache topology aware scheduling

[Alan Bateman]

On 10/09/2024 05:10, Danny Thomas wrote:
> I've switched to foreign functions for the native calls, using the 
> current CPU for external submissions, and a queuing threshold to 
> decide when to select the least loaded pool. Significantly improved 
> CPU utilization versus the default scheduler with a slight throughput 
> bump:
>
> https://github.com/DanielThomas/virtual-threads-cluster-aware/commit/c0e7b6141a84eb77e6848fa84014e7a98ddfc75b 
> <https://urldefense.com/v3/__https://github.com/DanielThomas/virtual-threads-cluster-aware/commit/c0e7b6141a84eb77e6848fa84014e7a98ddfc75b__;!!ACWV5N9M2RV99hQ!NYPwGwIo_GAtKLVsGpCxRAPgR40IvyvZFfG8b3prgbw7T9DAJqjaElA9yjBq1CaMR0Gef5W4FwxUK50Hxw$>
>
> I'll improve the benchmark to be lumpier with more submission pressure 
> to make work stealing more of a factor, and then look at balancing 
> with pollSubmission.
>

Good use of FFM.

You probably know this already: ForkJoinPool::getQueuedSubmissionCount 
is a O(n) scan so will be interesting to see how this performs as a 
heuristic.

Related is that ForkWorkWorkerThread has a method that tests two queues 
(local and "current source") as a cheap way to test if it could execute 
something immediately.  This is currently used by Exchanger and 
LinkedTransferQueue to influence whether to spin. Doug Lea has been 
thinking about whether to expose. Your experiments may be case that 
could use it.

-Alan
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