RE: [PATCH 0/3] mmc: renesas_sdhi_internal_dmac: improve performance by using IOMMU

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Hi Wolfram-san,

> From: Wolfram Sang, Sent: Friday, April 26, 2019 6:46 PM
> 
> Hi Shimoda-san,
> 
> thanks for working on this!
> 
> > Please refer to the end of this email about the performance.
> 
> Yes, nice improvements, great!

Thanks!

> > (I beleive if the performance is improved, the CPU load is also increased.)
> 
> I do wonder about this a bit, though. IPMMU and DMA shouldn't be that
> much expensive for the CPU, or? Am I overlooking something?

I'm guessing that a user land app (in this case bonnie++) consumes CPU load for some reason.
I'll experiment whether my guess is correct or not by using usb 3.0 host like below tomorrow:
 - case 1: usb 3.0 host + usb SSD as SuperSpeed (IOMMU is disabled).
 - case 2: usb 3.0 host + usb SSD via a usb2.0 hub as high-speed (IOMMU is disabled).

Best regards,
Yoshihiro Shimoda

> Kind regards,
> 
>    Wolfram





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