ide-tape: remove pipelined mode description from Documentation/ide/ide-tape.txt

 * interface, on the other hand, creates new requests, adds them

 * to the request-list of the block device, and waits for their completion.

 *

 * Pipelined operation mode is now supported on both reads and writes.

 *

 * The block device major and minor numbers are determined from the

 * tape's relative position in the ide interfaces, as explained in ide.c.

 *

 *

 * | Special care is recommended.  Have Fun!

 *

 *

 * An overview of the pipelined operation mode.

 *

 * In the pipelined write mode, we will usually just add requests to our

 * pipeline and return immediately, before we even start to service them. The

 * user program will then have enough time to prepare the next request while

 * we are still busy servicing previous requests. In the pipelined read mode,

 * the situation is similar - we add read-ahead requests into the pipeline,

 * before the user even requested them.

 *

 * The pipeline can be viewed as a "safety net" which will be activated when

 * the system load is high and prevents the user backup program from keeping up

 * with the current tape speed. At this point, the pipeline will get

 * shorter and shorter but the tape will still be streaming at the same speed.

 * Assuming we have enough pipeline stages, the system load will hopefully

 * decrease before the pipeline is completely empty, and the backup program

 * will be able to "catch up" and refill the pipeline again.

 *

 * When using the pipelined mode, it would be best to disable any type of

 * buffering done by the user program, as ide-tape already provides all the

 * benefits in the kernel, where it can be done in a more efficient way.

 * As we will usually not block the user program on a request, the most

 * efficient user code will then be a simple read-write-read-... cycle.

 * Any additional logic will usually just slow down the backup process.

 *

 * Using the pipelined mode, I get a constant over 400 KBps throughput,

 * which seems to be the maximum throughput supported by my tape.

 *

 * However, there are some downfalls:

 *

 *	1.	We use memory (for data buffers) in proportional to the number

 *		of pipeline stages (each stage is about 26 KB with my tape).

 *	2.	In the pipelined write mode, we cheat and postpone error codes

 *		to the user task. In read mode, the actual tape position

 *		will be a bit further than the last requested block.

 *

 * Concerning (1):

 *

 *	1.	We allocate stages dynamically only when we need them. When

 *		we don't need them, we don't consume additional memory. In

 *		case we can't allocate stages, we just manage without them

 *		(at the expense of decreased throughput) so when Linux is

 *		tight in memory, we will not pose additional difficulties.

 *

 *	2.	The maximum number of stages (which is, in fact, the maximum

 *		amount of memory) which we allocate is limited by the compile

 *		time parameter IDETAPE_MAX_PIPELINE_STAGES.

 *

 *	3.	The maximum number of stages is a controlled parameter - We

 *		don't start from the user defined maximum number of stages

 *		but from the lower IDETAPE_MIN_PIPELINE_STAGES (again, we

 *		will not even allocate this amount of stages if the user

 *		program can't handle the speed). We then implement a feedback

 *		loop which checks if the pipeline is empty, and if it is, we

 *		increase the maximum number of stages as necessary until we

 *		reach the optimum value which just manages to keep the tape

 *		busy with minimum allocated memory or until we reach

 *		IDETAPE_MAX_PIPELINE_STAGES.

 *

 * Concerning (2):

 *

 *	In pipelined write mode, ide-tape can not return accurate error codes

 *	to the user program since we usually just add the request to the

 *      pipeline without waiting for it to be serviced. In case an error

 *      occurs, I will report it on the next user request.

 *

 *	In the pipelined read mode, subsequent read requests or forward

 *	filemark spacing will perform correctly, as we preserve all blocks

 *	and filemarks which we encountered during our excess read-ahead.

 *

 *	For accurate tape positioning and error reporting, disabling

 *	pipelined mode might be the best option.

 *

 * You can enable/disable/tune the pipelined operation mode by adjusting

 * the compile time parameters below.

 *

 *

 *	Possible improvements.

 *

 *	1.	Support for the ATAPI overlap protocol.