Ensuring Transactional Ordering in I/O Agent

Techniques are disclosed relating to an I/O agent circuit. The I/O agent circuit may include one or more queues and a transaction pipeline. The I/O agent circuit may issue, to the transaction pipeline from a queue of the one or more queues, a transaction of a series of transactions enqueued in a particular order. The I/O agent circuit may generate, at the transaction pipeline, a determination to return the transaction to the queue based on a detection of one or more conditions being satisfied. Based on the determination, the I/O agent circuit may reject, at the transaction pipeline, up to a threshold number of transactions that issued from the queue after the transaction issued. The I/O agent circuit may insert the transaction at a head of the queue such that the transaction is enqueued at the queue sequentially first for the series of transactions according to the particular order.