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    Subject[PATCH v2 0/4] Add MMC software queue support
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    Hi All,

    Now the MMC read/write stack will always wait for previous request is
    completed by mmc_blk_rw_wait(), before sending a new request to hardware,
    or queue a work to complete request, that will bring context switching
    overhead, especially for high I/O per second rates, to affect the IO
    performance.

    Thus this patch set will introduce the MMC software command queue support
    based on command queue engine's interfaces, and set the queue depth as 2,
    that means we do not need wait for previous request is completed and can
    queue 2 requests in flight. It is enough to let the irq handler always
    trigger the next request without a context switch and then ask the blk_mq
    layer for the next one to get queued, as well as avoiding a long latency.

    Moreover we can expand the MMC software queue interface to support
    MMC packed request or packed command instead of adding new interfaces,
    according to previosus discussion.

    Below are some comparison data with fio tool. The fio command I used
    is like below with changing the '--rw' parameter and enabling the direct
    IO flag to measure the actual hardware transfer speed in 4K block size.

    ./fio --filename=/dev/mmcblk0p30 --direct=1 --iodepth=20 --rw=read --bs=4K --size=512M --group_reporting --numjobs=20 --name=test_read

    My eMMC card working at HS400 Enhanced strobe mode:
    [ 2.229856] mmc0: new HS400 Enhanced strobe MMC card at address 0001
    [ 2.237566] mmcblk0: mmc0:0001 HBG4a2 29.1 GiB
    [ 2.242621] mmcblk0boot0: mmc0:0001 HBG4a2 partition 1 4.00 MiB
    [ 2.249110] mmcblk0boot1: mmc0:0001 HBG4a2 partition 2 4.00 MiB
    [ 2.255307] mmcblk0rpmb: mmc0:0001 HBG4a2 partition 3 4.00 MiB, chardev (248:0)

    1. Without MMC software queue
    I tested 3 times for each case and output a average speed.

    1) Sequential read:
    Speed: 28.9MiB/s, 26.4MiB/s, 30.9MiB/s
    Average speed: 28.7MiB/s

    2) Random read:
    Speed: 18.2MiB/s, 8.9MiB/s, 15.8MiB/s
    Average speed: 14.3MiB/s

    3) Sequential write:
    Speed: 21.1MiB/s, 27.9MiB/s, 25MiB/s
    Average speed: 24.7MiB/s

    4) Random write:
    Speed: 21.5MiB/s, 18.1MiB/s, 18.1MiB/s
    Average speed: 19.2MiB/s

    2. With MMC software queue
    I tested 3 times for each case and output a average speed.

    1) Sequential read:
    Speed: 44.1MiB/s, 42.3MiB/s, 44.4MiB/s
    Average speed: 43.6MiB/s

    2) Random read:
    Speed: 30.6MiB/s, 30.9MiB/s, 30.5MiB/s
    Average speed: 30.6MiB/s

    3) Sequential write:
    Speed: 44.1MiB/s, 45.9MiB/s, 44.2MiB/s
    Average speed: 44.7MiB/s

    4) Random write:
    Speed: 45.1MiB/s, 43.3MiB/s, 42.4MiB/s
    Average speed: 43.6MiB/s

    Form above data, we can see the MMC software queue can help to improve the
    performance obviously.

    Any comments are welcome. Thanks a lot.

    Changes from v1:
    - Add request_done ops for sdhci_ops.
    - Replace virtual command queue with software queue for functions and
    variables.
    - Rename the software queue file and add sqhci.h header file.

    Baolin Wang (4):
    mmc: host: cqhci: Move the struct cqhci_slot into header file
    mmc: Add MMC software queue support
    mmc: host: sdhci: Add request_done ops for struct sdhci_ops
    mmc: host: sdhci-sprd: Add software queue support

    drivers/mmc/core/block.c | 61 ++++++++
    drivers/mmc/core/mmc.c | 13 +-
    drivers/mmc/core/queue.c | 25 ++-
    drivers/mmc/host/Kconfig | 9 ++
    drivers/mmc/host/Makefile | 1 +
    drivers/mmc/host/cqhci.c | 10 --
    drivers/mmc/host/cqhci.h | 17 +-
    drivers/mmc/host/sdhci-sprd.c | 26 ++++
    drivers/mmc/host/sdhci.c | 12 +-
    drivers/mmc/host/sdhci.h | 2 +
    drivers/mmc/host/sqhci.c | 345 +++++++++++++++++++++++++++++++++++++++++
    drivers/mmc/host/sqhci.h | 35 +++++
    include/linux/mmc/host.h | 3 +
    13 files changed, 536 insertions(+), 23 deletions(-)
    create mode 100644 drivers/mmc/host/sqhci.c
    create mode 100644 drivers/mmc/host/sqhci.h

    --
    1.7.9.5

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