I must code in some wrong way, multicore optimization cause performance degradation.

Here is my code framework:
10 strategy, 10 stock asset, 10 cpu cores
Each strategy only trade one stock asset.
preload=False, runonce=False

corenum = 10
stocknum = 10

class UserStockStrategy(bt.Strategy):
    def __init__(self):
        self.ind = MACD(self.datas[self.p.instance])
    def next(self):
        if time_is_right:
           self.buy(self.datas[self.p.instance])

cerebro = bt.Cerebro(preload=False, runonce=False, optdatas=False, maxcpus=corenum)
for i in range(corenum):
        params = (
            ('instance', i),
        )
        mydict = dict(params=params)
        MyStrategy = type( f'MyUserStockStrategy{i}', (UserStockStrategy,), mydict )
        setattr(bt.metabase, f'MyUserStockStrategy{i}', MyStrategy)
        cerebro.optstrategy(MyStrategy)

for i in range(stocknum):
        cerebro.adddata(pandas_data[i])
 
cerebro.run()

If not using multicore optimization, it need 50s to finish the task, if using muticore optimization, it need 60s.

Is there anything wrong in my code?

Thanks ind advance.

@vladisld Thank you very much. I forgot my password, so I have to register this account to come back online to express my thanks.

And I would like to try this path mentioned in your answer:
"I'm not sure it will work this way out of the box without violating some assumptions inside the Cerebro engine about proper sequence of calls to start,prenext,etc methods to be called as well as proper minperiod handling. However it is probably worth investigating in more details if one is willing to go this path."

Won't be a easy thing, but worth a try.

Sometime reply button also don't work, and there is some code on the page, like this:

$(document).ready(function () { app.coldLoad(); }); }

Hi
Somehow I forget my password, and apply to reset password. Then I got a password reset url link in email, but when I input new password and click the "reset" button, nothing happen. And I have to register another account to ask for help here.

Please help me, thanks.