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

[Philip Rakity]

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 believe ADMA will do large transfers.  Another data point.

Philip

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
> 
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