| 摘要 |
A read-to-write-back transaction may allow I/O subsystems (or other devices) to perform a write to a portion of a cache block without gaining ownership of the cache block and requiring that it respond to foreign requests for the cache block. In response to an I/O subsystem initiating a read-to-write-back transaction, the device owning the cache block conveys the cache block to the I/O subsystem, and the I/O subsystem may perform partial or entire writes to the cache block. Subsequently, the cache block is written back to a memory subsystem from the I/O subsystem. The system is implemented such that these operations may be viewed logically as an atomic operation with respect to other coherence transactions to the same cache block, and thus the I/O subsystem need not become the owner of the cache line during performance of the read-to-write-back transaction. Accordingly, the design of the I/O subsystem may be simplified while still providing the overall functionality as supported by the read-to-write-back transaction.
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