From mboxrd@z Thu Jan 1 00:00:00 1970 From: sourav.poddar@ti.com (Poddar, Sourav) Date: Thu, 30 Jun 2011 18:06:39 +0530 Subject: [PATCH v8 00/12] use nonblock mmc requests to minimize latency In-Reply-To: <1309248717-14606-1-git-send-email-per.forlin@linaro.org> References: <1309248717-14606-1-git-send-email-per.forlin@linaro.org> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Jun 28, 2011 at 1:41 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 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