Re: [PATCH v4 00/12] mmc: use nonblock mmc requests to minimize latency
From: S, Venkatraman
Date: Thu Jun 16 2011 - 09:40:00 EST
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:
> 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.
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