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

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

diff --git a/Documentation/ide/ide-tape.txt b/Documentation/ide/ide-tape.txt
index 658f271a373fca8c57dc50a32dc04ad494250fcf..51f596b282cd9537185242f23755d634c5a11b73 100644 (file)
--- a/Documentation/ide/ide-tape.txt
+++ b/Documentation/ide/ide-tape.txt
@@ -8,8 +8,6 @@
  * 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.
  *
@@ -45,83 +43,6 @@
  *
  * | 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.