Hello, Shaohua. > + list_splice_init(&q->flush_queue[q->flush_running_idx], &proceed_list); > + /* > + * If queue doesn't support queueable flush request, we can push the > + * pending requests to the next stage too. For such queue, there are no > + * normal requests running when flush request is running, so this still > + * guarantees the correctness. > + */ > + if (!blk_queue_flush_queueable(q)) > + list_splice_tail_init(&q->flush_queue[q->flush_pending_idx], > + &proceed_list); I can't see how this is safe. Request completion is decoupled from issue. What prevents low level driver from take in other requests before control hits here? And even if that holds for the current implementation, that's hardly something which can be guaranteed from !flush_queueable. Am I missing something? This kind of micro optimization is gonna bring very painful bugs which are extremely difficult to reproduce and track down. It scares the hell out of me. It's gonna silently skip flushes where it shouldn't. If you wanna optimize this case, a much better way would be implementing back-to-back flush optimization properly such that when block layer detects two flushes back-to-back and _KNOWS_ that no request has been issued inbetween, the second one is handled as noop. Mark the queue clean on flush, dirty on any other request and if the queue is clean all flushes can be completed immediately on issue which would also allow us to avoid the whole queue at the front or back issue without bothering low level drivers at all. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
