Re: [RFC PATCH v6 0/5] treewide: improve R-Car SDHI performance

[Wolfram Sang <wsa@the-dreams.de>]

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On Thu, Jun 13, 2019 at 07:20:10PM +0900, Yoshihiro Shimoda wrote:
> This patch series is based on iommu.git / next branch.
> 
> Since SDHI host internal DMAC of the R-Car Gen3 cannot handle two or
> more segments, the performance rate (especially, eMMC HS400 reading)
> is not good. However, if IOMMU is enabled on the DMAC, since IOMMU will
> map multiple scatter gather buffers as one contignous iova, the DMAC can
> handle the iova as well and then the performance rate is possible to
> improve. In fact, I have measured the performance by using bonnie++,
> "Sequential Input - block" rate was improved on r8a7795.
> 
> To achieve this, this patch series modifies IOMMU and Block subsystem
> at first. Since I'd like to get any feedback from each subsystem whether
> this way is acceptable for upstream, I submit it to treewide with RFC.
> 
> Changes from v5:
>  - Almost all patches are new code.
>  - [4/5 for MMC] This is a refactor patch so that I don't add any
>    {Tested,Reviewed}-by tags.
>  - [5/5 for MMC] Modify MMC subsystem to use bigger segments instead of
>    the renesas_sdhi driver.
>  - [5/5 for MMC] Use BLK_MAX_SEGMENTS (128) instead of local value
>    SDHI_MAX_SEGS_IN_IOMMU (512). Even if we use BLK_MAX_SEGMENTS,
>    the performance is still good.

Thanks for your hard work, Shimoda-san!

I may not be the biggest DMA, IOMMU, and block layer expert, but I
really like how this simplifies the SDHI driver and enhances the MMC
core. So, I'll add my two cents to the patches although I can't really
comment on the main functionality.


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