Re: [PATCH 0/5] mmc: add double buffering for mmc block requests

[Jaehoon Chung]

Hi Per..

it is interesting approach..so
we want to test your double buffering in our environment(Samsung SoC).

Did you test with SDHCI?
If you tested with SDHCI, i want to know how much increase the performance.

Thanks,
Jaehoon Chung

Per Forlin wrote:
> Add support to prepare one MMC request while another is active on
> the host. This is done by making the issue_rw_rq() asynchronous.
> The increase in throughput is proportional to the time it takes to
> prepare 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 U8500 on eMMC shows significant performance gain for DMA on MMC for large
> reads. In the PIO case there is some gain in performance for large reads too.
> There seems to be no or small performance gain for write, don't have a good
> explanation for this yet.
> 
> There are two optional hooks pre_req() and post_req() that the host driver
> may implement in order to improve double buffering. In the DMA case pre_req()
> may do dma_map_sg() and prepare the dma descriptor and post_req runs the
> dma_unmap_sg.
> 
> The mmci host driver implementation for double buffering is not intended
> nor ready for mainline yet. It is only an example of how to implement
> pre_req() and post_req(). The reason for this is that the basic DMA support
> for MMCI is not complete yet. The mmci patches are sent in a separate patch
> series "[FYI 0/4] arm: mmci: example implementation of double buffering".
> 
> Issues/Questions for issue_rw_rq() in block.c:
> * Is it safe to claim the host for the first MMC request and wait to release
>   it until the MMC queue is empty again? Or must the host be claimed and
>   released for every request?
> * Is it possible to predict the result from __blk_end_request().
>   If there are no errors for a completed MMC request and the
>   blk_rq_bytes(req) == data.bytes_xfered, will it be guaranteed that
>   __blk_end_request will return 0?
> 
> Here follows the IOZone results for u8500 v1.1 on eMMC.
> The numbers for DMA are a bit to good here due to the fact that the
> CPU speed is decreased compared to u8500 v2. This makes the cache handling
> even more significant.
> 
> Command line used: ./iozone -az -i0 -i1 -i2 -s 50m -I -f /iozone.tmp -e -R -+u
> 
> Relative diff: VANILLA-MMC-PIO -> 2BUF-MMC-PIO
> cpu load is abs diff
>                                                         random  random
>         KB      reclen  write   rewrite read    reread  read    write
>         51200   4       +0%     +0%     +0%     +0%     +0%     +0%
>         cpu:            +0.1    -0.1    -0.5    -0.3    -0.1    -0.0
> 
>         51200   8       +0%     +0%     +6%     +6%     +8%     +0%
>         cpu:            +0.1    -0.1    -0.3    -0.4    -0.8    +0.0
> 
>         51200   16      +0%     -2%     +0%     +0%     -3%     +0%
>         cpu:            +0.0    -0.2    +0.0    +0.0    -0.2    +0.0
> 
>         51200   32      +0%     +1%     +0%     +0%     +0%     +0%
>         cpu:            +0.1    +0.0    -0.3    +0.0    +0.0    +0.0
> 
>         51200   64      +0%     +0%     +0%     +0%     +0%     +0%
>         cpu:            +0.1    +0.0    +0.0    +0.0    +0.0    +0.0
> 
>         51200   128     +0%     +1%     +1%     +1%     +1%     +0%
>         cpu:            +0.0    +0.2    +0.1    -0.3    +0.4    +0.0
> 
>         51200   256     +0%     +0%     +1%     +1%     +1%     +0%
>         cpu:            +0.0    -0.0    +0.1    +0.1    +0.1    +0.0
> 
>         51200   512     +0%     +1%     +2%     +2%     +2%     +0%
>         cpu:            +0.1    +0.0    +0.2    +0.2    +0.2    +0.1
> 
>         51200   1024    +0%     +2%     +2%     +2%     +3%     +0%
>         cpu:            +0.2    +0.1    +0.2    +0.5    -0.8    +0.0
> 
>         51200   2048    +0%     +2%     +3%     +3%     +3%     +0%
>         cpu:            +0.0    -0.2    +0.4    +0.8    -0.5    +0.2
> 
>         51200   4096    +0%     +1%     +3%     +3%     +3%     +1%
>         cpu:            +0.2    +0.1    +0.9    +0.9    +0.5    +0.1
> 
>         51200   8192    +1%     +0%     +3%     +3%     +3%     +1%
>         cpu:            +0.2    +0.2    +1.3    +1.3    +1.0    +0.0
> 
>         51200   16384   +0%     +1%     +3%     +3%     +3%     +1%
>         cpu:            +0.2    +0.1    +1.0    +1.3    +1.0    +0.5
> 
> Relative diff: VANILLA-MMC-DMA -> 2BUF-MMC-MMCI-DMA
> cpu load is abs diff
>                                                         random  random
>         KB      reclen  write   rewrite read    reread  read    write
>         51200   4       +0%     -3%     +6%     +5%     +5%     +0%
>         cpu:            +0.0    -0.2    -0.6    -0.1    +0.3    +0.0
> 
>         51200   8       +0%     +0%     +7%     +7%     +7%     +0%
>         cpu:            +0.0    +0.1    +0.8    +0.6    +0.9    +0.0
> 
>         51200   16      +0%     +0%     +7%     +7%     +8%     +0%
>         cpu:            +0.0    -0.0    +0.7    +0.7    +0.8    +0.0
> 
>         51200   32      +0%     +0%     +8%     +8%     +9%     +0%
>         cpu:            +0.0    +0.1    +0.7    +0.7    +0.3    +0.0
> 
>         51200   64      +0%     +1%     +9%     +9%     +9%     +0%
>         cpu:            +0.0    +0.0    +0.8    +0.7    +0.8    +0.0
> 
>         51200   128     +1%     +0%     +13%    +13%    +14%    +0%
>         cpu:            +0.2    +0.0    +1.0    +1.0    +1.1    +0.0
> 
>         51200   256     +1%     +2%     +8%     +8%     +11%    +0%
>         cpu:            +0.0    +0.3    +0.0    +0.7    +1.5    +0.0
> 
>         51200   512     +1%     +2%     +16%    +16%    +17%    +0%
>         cpu:            +0.2    +0.2    +2.2    +2.1    +2.2    +0.1
> 
>         51200   1024    +1%     +2%     +20%    +20%    +20%    +1%
>         cpu:            +0.2    +0.1    +2.6    +1.9    +2.6    +0.0
> 
>         51200   2048    +0%     +2%     +22%    +22%    +21%    +0%
>         cpu:            +0.0    +0.3    +2.3    +2.9    +2.1    -0.0
> 
>         51200   4096    +1%     +2%     +23%    +23%    +23%    +1%
>         cpu:            +0.2    +0.1    +2.0    +3.2    +3.1    +0.0
> 
>         51200   8192    +1%     +5%     +24%    +24%    +24%    +1%
>         cpu:            +1.4    -0.0    +4.2    +3.0    +2.8    +0.1
> 
>         51200   16384   +1%     +3%     +24%    +24%    +24%    +2%
>         cpu:            +0.0    +0.3    +3.4    +3.8    +3.7    +0.1
> 
> Here follows the IOZone results for u5500 on eMMC.
> These numbers for DMA are more as expected.
> 
> Command line used: ./iozone -az -i0 -i1 -i2 -s 50m -I -f /iozone.tmp -e -R -+u
> 
> Relative diff: VANILLA-MMC-DMA -> 2BUF-MMC-MMCI-DMA
> cpu load is abs diff
>                                                         random  random
>         KB      reclen  write   rewrite read    reread  read    write
>         51200   128     +1%     +1%     +10%    +9%     +10%    +0%
>         cpu:            +0.1    +0.0    +1.3    +0.1    +0.8    +0.1
> 
>         51200   256     +2%     +2%     +7%     +7%     +9%     +0%
>         cpu:            +0.1    +0.4    +0.5    +0.6    +0.7    +0.0
> 
>         51200   512     +2%     +2%     +12%    +12%    +12%    +1%
>         cpu:            +0.4    +0.6    +1.8    +2.4    +2.4    +0.2
> 
>         51200   1024    +2%     +3%     +14%    +14%    +14%    +0%
>         cpu:            +0.3    +0.1    +2.1    +1.4    +1.4    +0.2
> 
>         51200   2048    +3%     +3%     +16%    +16%    +16%    +1%
>         cpu:            +0.2    +0.2    +2.5    +1.8    +2.4    -0.2
> 
>         51200   4096    +3%     +3%     +17%    +17%    +18%    +3%
>         cpu:            +0.1    -0.1    +2.7    +2.0    +2.7    -0.1
> 
>         51200   8192    +3%     +3%     +18%    +18%    +18%    +3%
>         cpu:            -0.1    +0.2    +3.0    +2.3    +2.2    +0.2
> 
>         51200   16384   +3%     +3%     +18%    +18%    +18%    +4%
>         cpu:            +0.2    +0.2    +2.8    +3.5    +2.4    -0.0
> 
> Per Forlin (5):
>   mmc: add member in mmc queue struct to hold request data
>   mmc: Add a block request prepare function
>   mmc: Add a second mmc queue request member
>   mmc: Store the mmc block request struct in mmc queue
>   mmc: Add double buffering for mmc block requests
> 
>  drivers/mmc/card/block.c |  337 ++++++++++++++++++++++++++++++----------------
>  drivers/mmc/card/queue.c |  171 +++++++++++++++---------
>  drivers/mmc/card/queue.h |   31 +++-
>  drivers/mmc/core/core.c  |   77 +++++++++--
>  include/linux/mmc/core.h |    7 +-
>  include/linux/mmc/host.h |    8 +
>  6 files changed, 432 insertions(+), 199 deletions(-)
> 
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