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. > 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
