On Thu, May 26, 2011 at 3:27 AM, 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 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 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 v3: > * Based on 2.6.39-rc7 > * Add error check for testlist in mmc_test.c > * Resolve in mmc-queue-thread that caused the mmc-thread to miss a wakeup. > * Move parallel request handling to core.c. This simplifies the interface > from 4 public functions to 1. This also gives access for SDIO to use the > same functionallity, even though the function is not tuned for the SDIO > execution flow yet. > > Per Forlin (12): > mmc: add none blocking mmc request function > 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() > 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: test: add random fault injection in core.c > mmc: add handling for two parallel block requests in issue_rw_rq > > drivers/mmc/card/block.c | 452 +++++++++++++++++++++++++---------------- > drivers/mmc/card/mmc_test.c | 361 ++++++++++++++++++++++++++++++++- > drivers/mmc/card/queue.c | 184 +++++++++++------ > drivers/mmc/card/queue.h | 32 +++- > drivers/mmc/core/core.c | 165 ++++++++++++++- > 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 | 6 +- > include/linux/mmc/host.h | 19 ++ > lib/Kconfig.debug | 11 + > 12 files changed, 1187 insertions(+), 292 deletions(-) > Nitpick.. The mmc_test.c changes should be at the end of the series, after the async feature is available. Regards, Venkat. -- 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
