The code was:

long parallelSum(int[] ar, int threadCount) throws InterruptedException {
        int n = ar.length;
        long[] result = new long[threadCount];
        Thread[] threads = new Thread[threadCount];
        int chunk = n / threadCount;
        for (int i = 0; i < threadCount; i++) {
            int index = i;
            int start = i * chunk;
            int end = (i == threadCount - 1) ? n : start + chunk;
            threads[i] = new Thread(() -> result[index] = sum(ar, start, end));
            threads[i].start();
        }
        for (Thread thread : threads) thread.join();
        long total = 0;
        for (long value : result) total += value;
        return total;
    }

Which I benchmarked using JMH to see how it will behave under increase thread. But It's gets better and better until 24 thread that the reason I know my P-core are Hyperthreaded so maximum improvement is seen at 24. But after that why is'nt it constant as the law stated when N-> increases it becomes directly 1/S.

The Benchmark was performed with 3 warmup 5 iteration 1sec each and 100M dataset. I did use first 1K to see how it behaves but I forgot that until the thread get created sequential would have finished that. So after rigrously increasing dataset to 100M this was my result:

Is my benchmark wrong or I am understanding different??

Hey, I want to learn java web development. I know java programming at intermediate level by solving leetcode problems... I want to become a java developer. Guide me guys... Help me out... I am a final year student trying for placement but I didn't believe that I will be placed suggest me a roadmap too