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