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

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Hi Wolfram-san again,

> From: Yoshihiro Shimoda, Sent: Tuesday, May 7, 2019 5:59 PM
> 
> 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).

I have measured them + IOMMU enabled environment. It seems my guess is correct.

  - 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).
  - case 3: usb 3.0 host + usb SSD as SuperSpeed (IOMMU is enabled).
  - case 4: usb 3.0 host + usb SSD via a usb2.0 hub as high-speed (IOMMU is enabled).

---
kernel v5.1-rc7 + local patches + USB SSD ext4 format,,,,,,,,,,,,,,,,,,,,,,,,,,
Buildroot 2019.02.1,,,,,,,,,,,,,,,,,,,,,,,,,,
Bonnie++ 1.03e : bonnie\+\+ -d ./ -s 8192 -r 4096 -b -u root,,,,,,,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,,,,,,,
environment,Size,Sequential Output - per char (K/sec),<- (CPU %),Sequential Output - block (K/sec),<- (CPU %),Sequential Output - rewrite (K/sec),<- (CPU %),Sequential Input - per char (K/sec),<- (CPU %),Sequential Input ? block (K/sec),<- (CPU %),Random seeks,<- (CPU %),files,Sequential Create,<- (CPU %),Sequential Read,<- (CPU %),Sequential Delete,<- (CPU %),Random Create,<- (CPU %),Random Read,<- (CPU %),Random Delete,<- (CPU %)
H3_SuperSpeed_No_IOMMU,8G,82598,99,242161,58,102489,25,73719,98,254089,32,2133.3,6,16,382,2,+++++,+++,385,1,380,1,+++++,+++,387,2
H3_HighSpeed_No_IOMMU,8G,41971,53,39983,9,16459,4,37900,51,37833,5,1585.7,5,16,304,1,+++++,+++,295,1,302,1,+++++,+++,294,1
H3_SuperSpeed_IOMMU,8G,66139,99,276686,65,132297,33,69732,99,293396,37,2099.2,7,16,389,2,+++++,+++,391,1,382,1,+++++,+++,391,2
H3_HighSpeed_IOMMU,8G,43191,50,40446,9,17432,4,38541,51,38481,5,1619.4,4,16,302,1,+++++,+++,296,1,303,1,+++++,+++,294,1
---

Best regards,
Yoshihiro Shimoda





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