Multiprocessing - low CPU usage when more than 2 cores

[medatib531]

Hello,
I'm trying to understand how multiprocessing-multithreading works. Suppose I have the following code (which is basically the idea behind mining). In this case I am using 2 cores and everything looks good.
However if I choose to use more cores, the CPU utilization drops. i.e. if I use 4 cores, it utilizes them at 50% each. If I use 8, it utilizes them at 25% and so on.
My CPU is i9-9980HK 8-core.
Thank you

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import hashlib import time import multiprocessing as mp def hash_string(string):     """     Return a SHA-256 hash of the given string     """     return hashlib.sha256(string.encode('utf-8')).hexdigest()     def mine(seed,quit,foundit):     #start = time.time()     while not quit.is_set():         test = hash_string(str(seed) + "Teststring")         seed +=1         if test[0:6] == '000000':             print(test)             print(seed)             #print("Total time:" + str(time.time() - start))             foundit.set()             break   import multiprocessing as mp quit = mp.Event() foundit = mp.Event() start = time.time() #for i in range(int(mp.cpu_count()/2)): for i in range(2):     p = mp.Process(target=mine, args=((i+2)*100000000, quit, foundit))     p.start() foundit.wait() quit.set() print("Total time:" + str(time.time() - start))