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

[Jaehoon Chung]

Hi Philip..

I have something question..did you test SDMA and ADMA?

Actually i didn't test [patch v3] but i tested patch v2 before Per sent.
I got that SDMA is faster than ADMA. (using bounce buffer and sdhci)

How do you think about that? I want to know your thought.
And if you can share the results, i want to know them.

Regards,
Jaehoon Chung


Philip Rakity wrote:
> On May 9, 2011, at 5:34 AM, Per Forlin wrote:
> 
>> On 9 May 2011 04:05, Philip Rakity <prakity at 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
>>>>
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>>>
> 
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