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Introducing TLB Middleware in Akita

· 2 min read
Daoxuan Xu
Daoxuan Xu
Undergraduate Student
Huizhi Zhao
Huizhi Zhao
Undergraduate Student

The Translation Lookaside Buffer (TLB) is a crucial component in virtual memory systems that speeds up virtual-to-physical address translation. We have updated the tlb package with our “drain-flush-restart” protocol and implemented middlewares to support higher modularity, flexibility, and efficiency.

tlbMiddleware is responsible for managing and executing all internal TLB requests and tasks. It is designed to operate in a pipelined manner, processing up to multiple requests per cycle and maintaining internal state for control flow.

Problems​

TLB only supports 1-cycle latency when processing requests. Control messages and operational requests are not diversified. TLB functionalities are concentrated and lengthy.

Work Principle​

Key Components and Features​

A. ControlPort Handling(Flush/Restart/switch): Manages incoming control messages, enables reaction to system-level control.

B. State Machine(Enable/Drain/Pause): Specifies actions under different circumstances, ensures that the component works properly if simulation process is somehow paused or stopped.

C. Pipeline: Operates as an intermediate queue to enable multiple requests to be processed.

Ticking Flow​

The basic flow of the tlbMiddleware is as follows:

For each "Ticking" cycle, tlbMiddleware first peeks into the controlPort and performs the control message to either perform Flush/Restart or switch the state of tlbMiddleware between enable/drain/pause.

According to its current state, the middleware executes state-dependent behavior: enabled, draining, or paused.

  • In the enable state, the middleware first tries to retrieve and send responded MSHR entries to top via respondMSHREntry(). Then, it parses incoming translation responses from lower memory via parseBottom(). After generating responses, it ticks the pipeline to retrieve new translation requests and process requests in line via lookup().

  • In the drain state, the middleware does similar cyclic tasks as in the enable state, where it responds to completed MSHR entries and parses incoming translation responses from lower memory. However, when ticking the pipeline, it no longer fetches new requests and only processes remaining requests in the pipeline. After both MSHR and bottomPort are drained to empty, the state will be switched to pause.

  • In the pause state, the middleware does nothing.

With pipeline and actions regulated by different states, tlbMiddleware improves the efficiency of the TLB component in handling requests in parallel.