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    Subject[PATCH v4 00/12] mmc: use nonblock mmc requests to minimize latency
    How significant is the cache maintenance over head?
    It depends, the eMMC are much faster now
    compared to a few years ago and cache maintenance cost more due to
    multiple cache levels and speculative cache pre-fetch. In relation the
    cost for handling the caches have increased and is now a bottle neck
    dealing with fast eMMC together with DMA.

    The intention for introducing none blocking mmc requests is to minimize the
    time between a mmc request ends and another mmc request starts. In the
    current implementation the MMC controller is idle when dma_map_sg and
    dma_unmap_sg is processing. Introducing none blocking mmc request makes it
    possible to prepare the caches for next job parallel with an active
    mmc request.

    This is done by making the issue_rw_rq() none blocking.
    The increase in throughput is proportional to the time it takes to
    prepare (major part of preparations is dma_map_sg and dma_unmap_sg)
    a request and how fast the memory is. The faster the MMC/SD is
    the more significant the prepare request time becomes. Measurements on U5500
    and Panda on eMMC and SD shows significant performance gain for large
    reads when running DMA mode. In the PIO case the performance is unchanged.

    There are two optional hooks pre_req() and post_req() that the host driver
    may implement in order to move work to before and after the actual mmc_request
    function is called. In the DMA case pre_req() may do dma_map_sg() and prepare
    the dma descriptor and post_req runs the dma_unmap_sg.

    Details on measurements from IOZone and mmc_test:

    Changes since v3:
    * Based on 2.6.39-rc7
    * Add error check for testlist in mmc_test.c
    * Resolve in mmc-queue-thread that caused the mmc-thread to miss a wakeup.
    * Move parallel request handling to core.c. This simplifies the interface
    from 4 public functions to 1. This also gives access for SDIO to use the
    same functionallity, even though the function is not tuned for the SDIO
    execution flow yet.

    Per Forlin (12):
    mmc: add none blocking mmc request function
    omap_hsmmc: use original sg_len for dma_unmap_sg
    omap_hsmmc: add support for pre_req and post_req
    mmci: implement pre_req() and post_req()
    mmc: mmc_test: add debugfs file to list all tests
    mmc: mmc_test: add test for none blocking transfers
    mmc: add member in mmc queue struct to hold request data
    mmc: add a block request prepare function
    mmc: move error code in mmc_block_issue_rw_rq to a separate function.
    mmc: add a second mmc queue request member
    mmc: test: add random fault injection in core.c
    mmc: add handling for two parallel block requests in issue_rw_rq

    drivers/mmc/card/block.c | 452 +++++++++++++++++++++++++----------------
    drivers/mmc/card/mmc_test.c | 361 ++++++++++++++++++++++++++++++++-
    drivers/mmc/card/queue.c | 184 +++++++++++------
    drivers/mmc/card/queue.h | 32 +++-
    drivers/mmc/core/core.c | 165 ++++++++++++++-
    drivers/mmc/core/debugfs.c | 5 +
    drivers/mmc/host/mmci.c | 146 ++++++++++++--
    drivers/mmc/host/mmci.h | 8 +
    drivers/mmc/host/omap_hsmmc.c | 90 ++++++++-
    include/linux/mmc/core.h | 6 +-
    include/linux/mmc/host.h | 19 ++
    lib/Kconfig.debug | 11 +
    12 files changed, 1187 insertions(+), 292 deletions(-)


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