On Tue, Jun 28, 2011 at 1:41 PM, Per Forlin <per.forlin@xxxxxxxxxx> 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@xxxxxx> -- 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
