[PATCH v3 0/3] Add MMC software queue support

[Baolin Wang]

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 v2:
 - Remove reference to 'struct cqhci_host' and 'struct cqhci_slot',
 instead adding 'struct sqhci_host', which is only used by software queue.

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 (3):
  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/sdhci-sprd.c |   26 ++++
 drivers/mmc/host/sdhci.c      |   12 +-
 drivers/mmc/host/sdhci.h      |    2 +
 drivers/mmc/host/sqhci.c      |  344 +++++++++++++++++++++++++++++++++++++++++
 drivers/mmc/host/sqhci.h      |   53 +++++++
 include/linux/mmc/host.h      |    3 +
 11 files changed, 537 insertions(+), 12 deletions(-)
 create mode 100644 drivers/mmc/host/sqhci.c
 create mode 100644 drivers/mmc/host/sqhci.h

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1.7.9.5