Hello, all. I went through libata-convert-to-block-tagging today and found several issues. 1. libata internal data structure for command context (qc) allocation is bound to tag allocation, which means that block layer tagging should be enabled for all controllers which have can_queue > 1. 2. blk-tag offsets allocation for non-sync requests. I'm not confident this is safe. Till now, if there was only single command in flight for the port, it was guaranteed that the qc gets tag zero whether the device is NCQ capable or not. qc allocation is tied tightly with hardware command slot allocation and I don't think it's wise to change this assumption. #1 is easy to fix but #2 requires either adding a spinlock or two atomic variables to struct blk_queue_tag to keep the current behavior while guaranteeing that tags are used in order. Also, there's delay between libata marks a request complete and the request actually gets completed and the tag is freed. If another request gets issued inbetween, the tag number can't be guaranteed. This can be worked around by re-mapping tag number in libata depending on command type but, well then, it's worse than the original implementation. So, please revert the following commits. 43a49cbdf31e812c0d8f553d433b09b421f5d52c e013e13bf605b9e6b702adffbe2853cfc60e7806 2fca5ccf97d2c28bcfce44f5b07d85e74e3cd18e 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
