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    SubjectRe: [PATCH v3 00/12] mmc: use nonblock mmc requests to minimize latency

    On May 9, 2011, at 5:34 AM, Per Forlin wrote:

    > On 9 May 2011 04:05, Philip Rakity <prakity@marvell.com> wrote:
    >>
    >> Hi Per,
    >>
    >> We noticed on some of our systems if we ADMA or SDMA and a bounce buffer it is significantly faster then SDMA.
    >>
    > I have not done work with ADMA or SDMA. Where should I look to read
    > more about it?
    > Are these the right places. DMA iop-dma.c and imx-sdma.c, MMC: sdhci.c.

    sdhci.c for ADMA and SDMA

    spec is at
    http://www.sdcard.org/developers/tech/sdcard/pls/simplified_specs/

    version 3 discusses ADMA

    >
    >> I believe ADMA will do large transfers. Another data point.
    >>
    >> Philip
    > Thanks,
    > Per
    >
    >>
    >> On May 7, 2011, at 12:14 PM, Per Forlin wrote:
    >>
    >>> 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 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:
    >>> https://wiki.linaro.org/WorkingGroups/Kernel/Specs/StoragePerfMMC-async-req
    >>>
    >>> Under consideration:
    >>> * Make pre_req and post_req private to core.c.
    >>> * Generalize implementation and make it available for SDIO.
    >>>
    >>> Changes since v2:
    >>> * Fix compile warnings in core.c and block.c
    >>> * Simplify max transfer size in mmc_test
    >>> * set TASK_RUNNING in queue.c before issue_req()
    >>>
    >>> Per Forlin (12):
    >>> mmc: add none blocking mmc request function
    >>> 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: add handling for two parallel block requests in issue_rw_rq
    >>> mmc: test: add random fault injection in core.c
    >>> 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()
    >>>
    >>> drivers/mmc/card/block.c | 493 +++++++++++++++++++++++++++--------------
    >>> drivers/mmc/card/mmc_test.c | 340 +++++++++++++++++++++++++++-
    >>> drivers/mmc/card/queue.c | 180 ++++++++++------
    >>> drivers/mmc/card/queue.h | 31 ++-
    >>> drivers/mmc/core/core.c | 132 ++++++++++-
    >>> 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 | 9 +-
    >>> include/linux/mmc/host.h | 13 +-
    >>> lib/Kconfig.debug | 11 +
    >>> 12 files changed, 1174 insertions(+), 284 deletions(-)
    >>>
    >>> --
    >>> 1.7.4.1
    >>>
    >>> --
    >>> To unsubscribe from this list: send the line "unsubscribe linux-mmc" in
    >>> the body of a message to majordomo@vger.kernel.org
    >>> More majordomo info at http://vger.kernel.org/majordomo-info.html
    >>
    >>



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