Rock (processor) - Unconventional Features

Unconventional Features

In 2005, Sun publicly disclosed a feature in the Rock processor called hardware scout. Hardware scout uses otherwise idle chip execution resources to perform prefetching during cache misses.

In March 2006, Marc Tremblay, Vice President and Chief Architect for Sun's Scalable Systems Group, gave a presentation at the Xerox Palo Alto Research Center (PARC) on thread-level parallelism, hardware scouting, and thread-level speculation. These multithreading technologies were expected to be included in the Rock processor.

In August 2007, Sun confirmed that Rock would be the first production processor to support transactional memory. To provide the functionality, two new instructions were introduced (chkpt, commit) with one new status register (cps). The instruction chkpt is used to begin a transaction and commit to commit the transaction. If transaction abort condition is detected, jump to is issued and cps can be used to determine the reason. The support is best-effort based, as in addition to data conflicts, transactions can be aborted by other reasons. These include TLB misses, interrupts, certain commonly used function call sequences and "difficult" instructions (e.g., division). Nevertheless, many (arguably fine-grained) code blocks requiring synchronization could have benefited from transactional memory support of the Rock processor.

In February 2008, Marc Tremblay announced a unique feature called "out-of-order retirement" at the ISSCC. The benefits include replacing the "traditional instruction window with this much smaller deferred queue".

In April 2008, Sun engineers presented the transactional memory interface at Transact 2008, and the Adaptive Transactional Memory Test Platform simulator was announced to be made available to the general public shortly after.