Re: eMMC performance regression caused by 427b6514d0953bf

[Jisheng Zhang <Jisheng.Zhang@synaptics.com>]

On Tue, 13 Oct 2020 16:23:36 +0300 Adrian Hunter wrote:

> 
> On 13/10/20 3:32 pm, Ulf Hansson wrote:
> > + Adrian
> >
> > On Tue, 13 Oct 2020 at 13:09, Jisheng Zhang <Jisheng.Zhang@synaptics.com> wrote:  
> >>
> >> Hi,
> >>
> >> I found an emmc performance regression with below simple benchmark cmd:
> >>
> >> dd if=/dev/mmcblk0 of=/dev/null bs=8192 count=100000
> >>
> >> This regression has been bisected to commit
> >> 427b6514d0953bf (“mmc: sdhci: Add Auto CMD Auto Select support”)
> >>
> >> If I revert this commit, the performance is good now.
> >>
> >> I’m not sure whether this is common issue or not.  
> >
> > Can you provide some data, like how much is the regression and how
> > many tests did you run?

before the commit, 120MB/s
after the commit, 51.3MB/s

tested 10 times

> >
> > Did you try different block sizes of the dd command?  
> 
> Also what is the SDHCI version?  The patch in question is for version >= 4.1

V4.2

> 
> What driver?

sdhci-of-dwcmshc.c, but some phy tuning code isn't mainlined yet.

> 
> Can you tell if the patch changed which auto command is used?

autocmd23

Now I have a fix, the Auto CMD auto Select can only be used when v4 mode
is enabled. Although the HW supports v4.1, but drivers may haven't enabled
it due to various reasons. I just sent out the fix a few minutes ago.


Thanks