[PATCH v8 00/12] use nonblock mmc requests to minimize latency

[S, Venkatraman]

On Thu, Jun 30, 2011 at 6:06 PM, Poddar, Sourav <sourav.poddar at ti.com> wrote:
> On Tue, Jun 28, 2011 at 1:41 PM, Per Forlin <per.forlin at linaro.org> 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 non-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 non-blocking mmc request makes it
>> possible to prepare the caches for next job in parallel to an active
>> mmc request.
>>
>> This is done by making the issue_rw_rq() non-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:
>> https://wiki.linaro.org/WorkingGroups/Kernel/Specs/StoragePerfMMC-async-req
>>
>> Changes since v7:
>>  * rebase on mmc-next, on top of Russell's updated error handling.
>>  * Clarify description of mmc_start_req()
>>  * Resolve compile without CONFIG_DMA_ENIGNE issue for mmci
>>  * Add mmc test to measure how performance is affected by sg length
>>  * Add missing wait_for_busy in mmc_test non-blocking test. This call got lost
>>   in v4 of this patchset when refactoring mmc_start_req.
>>  * Add sub-prefix (core block queue) to relevant patches.
>>
>> Per Forlin (12):
>>  mmc: core: add non-blocking mmc request function
>>  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 non-blocking transfers
>>  mmc: mmc_test: test to measure how sg_len affect performance
>>  mmc: block: add member in mmc queue struct to hold request data
>>  mmc: block: add a block request prepare function
>>  mmc: block: move error code in issue_rw_rq to a separate function.
>>  mmc: queue: add a second mmc queue request member
>>  mmc: core: add random fault injection
>>  mmc: block: add handling for two parallel block requests in
>>    issue_rw_rq
>>
>>  drivers/mmc/card/block.c      |  505 ++++++++++++++++++++++++-----------------
>>  drivers/mmc/card/mmc_test.c   |  491 ++++++++++++++++++++++++++++++++++++++--
>>  drivers/mmc/card/queue.c      |  184 ++++++++++------
>>  drivers/mmc/card/queue.h      |   33 ++-
>>  drivers/mmc/core/core.c       |  167 +++++++++++++-
>>  drivers/mmc/core/debugfs.c    |    5 +
>>  drivers/mmc/host/mmci.c       |  147 +++++++++++-
>>  drivers/mmc/host/mmci.h       |    8 +
>>  drivers/mmc/host/omap_hsmmc.c |   87 +++++++-
>>  include/linux/mmc/core.h      |    6 +-
>>  include/linux/mmc/host.h      |   24 ++
>>  lib/Kconfig.debug             |   11 +
>>  12 files changed, 1345 insertions(+), 323 deletions(-)
>
>
>
> Boot tested on Omap4430 Blaze board.
>
> Tested-by: Sourav Poddar<sourav.poddar at ti.com>
>
Reviewed for OMAP along with Sourav's tests..
Reviewed-by: Venkatraman S <svenkatr at ti.com>