Microprocessor with improved data stream prefetching

Abstract

A microprocessor with multiple stream prefetch engines each executing a stream prefetch instruction to prefetch a complex data stream specified by the instruction in a manner synchronized with program execution of loads from the stream is provided. The stream prefetch engine stays at least a fetch-ahead distance (specified in the instruction) ahead of the program loads, which may randomly access the stream. The instruction specifies a level in the cache hierarchy to prefetch into, a locality indicator to specify the urgency and ephemerality of the stream, a stream prefetch priority, a TLB miss policy, a page fault miss policy, a protection violation policy, and a hysteresis value, specifying a minimum number of bytes to prefetch when the stream prefetch engine resumes prefetching. The memory subsystem includes a separate TLB for stream prefetches; or a joint TLB backing the stream prefetch TLB and load/store TLB; or a separate TLB for each prefetch engine.