|author||Borislav Petkov <email@example.com>||2008-04-27 15:38:28 +0200|
|committer||Bartlomiej Zolnierkiewicz <firstname.lastname@example.org>||2008-04-27 15:38:28 +0200|
ide-tape: remove pipelined mode description from Documentation/ide/ide-tape.txt
Signed-off-by: Borislav Petkov <email@example.com> Signed-off-by: Bartlomiej Zolnierkiewicz <firstname.lastname@example.org>
Diffstat (limited to 'Documentation')
1 files changed, 0 insertions, 79 deletions
diff --git a/Documentation/ide/ide-tape.txt b/Documentation/ide/ide-tape.txt
index 658f271a373f..51f596b282cd 100644
@@ -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.