scsi: target: Allow userspace to request direct submissions

This allows userspace to request the fabric drivers do direct submissions if they support it. With the new device file, submit_type, users can write 0 - 2 to control how commands are submitted to the backend: 0 - TARGET_FABRIC_DEFAULT_SUBMIT - LIO will use the fabric's default submission type. This is the default for compat. 1 - TARGET_DIRECT_SUBMIT - LIO will submit the cmd to the backend from the calling context if the fabric the cmd was received on supports it, else it will use the fabric's default type. 2 - TARGET_QUEUE_SUBMIT - LIO will queue the cmd to the LIO submission workqueue which will pass it to the backend. When using an NVMe drive and vhost-scsi with direct submission we see around a 20% improvement in 4K I/Os: fio jobs 1 2 4 8 10 -------------------------------------------------- defer 94K 190K 394K 770K 890K direct 128K 252K 488K 950K - And when using the queueing mode, we now no longer see issues like where the iSCSI tx thread is blocked in the block layer waiting on a tag so it can't respond to a nop or perform I/Os for other LUs.

Mike Christie committed 3 years ago

Commit e2f4ea41 parent 42892676 files · +57 −12Browse files

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include/target/target_core_base.h+1−0

@@ -726,6 +726,7 @@ struct se_dev_attrib { · 725 unmodified lines
726	u32 unmap_granularity;	726	u32 unmap_granularity;
727	u32 unmap_granularity_alignment;	727	u32 unmap_granularity_alignment;
728	u32 max_write_same_len;	728	u32 max_write_same_len;
		729	u8 submit_type;
729	struct se_device *da_dev;	730	struct se_device *da_dev;
730	struct config_group da_group;	731	struct config_group da_group;
731	};	732	};