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@@ -8,8 +8,6 @@
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* interface, on the other hand, creates new requests, adds them
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* to the request-list of the block device, and waits for their completion.
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*
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- * Pipelined operation mode is now supported on both reads and writes.
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- *
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* The block device major and minor numbers are determined from the
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* tape's relative position in the ide interfaces, as explained in ide.c.
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*
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@@ -45,83 +43,6 @@
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*
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* | Special care is recommended. Have Fun!
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*
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- *
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- * An overview of the pipelined operation mode.
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- *
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- * In the pipelined write mode, we will usually just add requests to our
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- * pipeline and return immediately, before we even start to service them. The
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- * user program will then have enough time to prepare the next request while
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- * we are still busy servicing previous requests. In the pipelined read mode,
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- * the situation is similar - we add read-ahead requests into the pipeline,
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- * before the user even requested them.
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- *
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- * The pipeline can be viewed as a "safety net" which will be activated when
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- * the system load is high and prevents the user backup program from keeping up
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- * with the current tape speed. At this point, the pipeline will get
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- * shorter and shorter but the tape will still be streaming at the same speed.
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- * Assuming we have enough pipeline stages, the system load will hopefully
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- * decrease before the pipeline is completely empty, and the backup program
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- * will be able to "catch up" and refill the pipeline again.
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- *
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- * When using the pipelined mode, it would be best to disable any type of
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- * buffering done by the user program, as ide-tape already provides all the
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- * benefits in the kernel, where it can be done in a more efficient way.
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- * As we will usually not block the user program on a request, the most
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- * efficient user code will then be a simple read-write-read-... cycle.
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- * Any additional logic will usually just slow down the backup process.
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- *
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- * Using the pipelined mode, I get a constant over 400 KBps throughput,
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- * which seems to be the maximum throughput supported by my tape.
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- *
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- * However, there are some downfalls:
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- *
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- * 1. We use memory (for data buffers) in proportional to the number
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- * of pipeline stages (each stage is about 26 KB with my tape).
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- * 2. In the pipelined write mode, we cheat and postpone error codes
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- * to the user task. In read mode, the actual tape position
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- * will be a bit further than the last requested block.
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- *
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- * Concerning (1):
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- *
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- * 1. We allocate stages dynamically only when we need them. When
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- * we don't need them, we don't consume additional memory. In
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- * case we can't allocate stages, we just manage without them
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- * (at the expense of decreased throughput) so when Linux is
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- * tight in memory, we will not pose additional difficulties.
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- *
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- * 2. The maximum number of stages (which is, in fact, the maximum
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- * amount of memory) which we allocate is limited by the compile
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- * time parameter IDETAPE_MAX_PIPELINE_STAGES.
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- *
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- * 3. The maximum number of stages is a controlled parameter - We
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- * don't start from the user defined maximum number of stages
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- * but from the lower IDETAPE_MIN_PIPELINE_STAGES (again, we
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- * will not even allocate this amount of stages if the user
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- * program can't handle the speed). We then implement a feedback
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- * loop which checks if the pipeline is empty, and if it is, we
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- * increase the maximum number of stages as necessary until we
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- * reach the optimum value which just manages to keep the tape
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- * busy with minimum allocated memory or until we reach
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- * IDETAPE_MAX_PIPELINE_STAGES.
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- *
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- * Concerning (2):
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- *
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- * In pipelined write mode, ide-tape can not return accurate error codes
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- * to the user program since we usually just add the request to the
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- * pipeline without waiting for it to be serviced. In case an error
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- * occurs, I will report it on the next user request.
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- *
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- * In the pipelined read mode, subsequent read requests or forward
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- * filemark spacing will perform correctly, as we preserve all blocks
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- * and filemarks which we encountered during our excess read-ahead.
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- *
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- * For accurate tape positioning and error reporting, disabling
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- * pipelined mode might be the best option.
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- *
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- * You can enable/disable/tune the pipelined operation mode by adjusting
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- * the compile time parameters below.
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- *
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- *
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* Possible improvements.
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*
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* 1. Support for the ATAPI overlap protocol.
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Borislav Petkov