Speculative Data Cache

    This cache implements the write-back policy. A new “Speculative” state is added to each line. This allows the cache to differentiate cache blocks that was written after a checkpoint was taken. If a speculative block has to be evicted, the corresponding block in the next lower hierarchy will be marked as “Speculative”.

    However if the following level is the main memory or a normal cache, then the checkpoint will be discarded and all blocks in “Speculative” state will be changed to “Dirty”. This effectively commits all operations after a checkpoint. On the event of a rollback, every speculative cache block will be invalidated.

    The proposed design allows quick checkpoint taking. On the other hand, rolling back or committing a checkpoint is very expensive because a full traversal of the cache is needed.