Runahead - Register File Checkpoint Options

Register File Checkpoint Options

The most obvious method of checkpointing the register file (RF) is to simply perform a flash copy to a shadow register file, or backup register file (BRF) when the processor enters runahead mode, then perform a flash copy from the BRF to the RF when normal operation resumes. There are simpler options available.

One way to eliminate the flash copy operations is to write to both the BRF and RF during normal operation, read from only the RF during normal operation, and read/write only the BRF during runahead mode.

An even more aggressive approach is to eliminate the BRF and rely upon the forwarding paths to provide modified values during runahead mode. Checkpointing is accomplished by disabling register file writes. Modified values during runahead mode can only be provided by the forwarding paths.

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