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 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-mmc" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
