Core assignment in SQL server

Hi,

Could anybody help me, when configure core in SQL, do we need to leave any specific number of Cores to OS and remaining for SQL, so that we can buy that many number of core license for SQL?. Or we can assign all the Cores available to SQL Server. How will be performance impact at OS level if all the available cares are assigned for SQL?. Any article or suggestions.

Thanks,

Ashru

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