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

[sourav.poddar@ti.com (Poddar, Sourav)]

On Tue, Jun 28, 2011 at 1:41 PM, Per Forlin <per.forlin@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@ti.com>