Powershell:Set-SPEnterpriseSearchService -PerformanceLevel Reduced
Specifies the relative number of threads for the crawl component performance:
Reduced: Total number of threads = number of processors, Max Threads/host = number of processors
Partly Reduced: Total number of threads = 4 times the number of processors , Max Threads/host = 16 time the number of processors
Maximum: Total number of threads = number of processors
The type must be one of the following values: Reduced,PartlyReduced, or Maximum