Re: [PATCH 07/17] mmc: sdhci: avoid unnecessary mapping/unmapping of align buffer

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On Mon, Dec 21, 2015 at 11:28:15AM +0100, Ulf Hansson wrote:
> On 19 December 2015 at 21:30, Russell King <rmk+kernel@xxxxxxxxxxxxxxxx> wrote:
> > Unnecessarily mapping and unmapping the align buffer for SD cards is
> > expensive: performance measurements on iMX6 show that this gives a hit
> > of 10% on hdparm buffered disk reads.
> >
> > MMC/SD card IO comes from the mm/vfs which gives us page based IO, so
> > for this case, the align buffer is not going to be used.  However, we
> > still map and unmap this buffer.
> 
> What about the SDIO case? How will this change affect SDIO data transfers?

I can't quantify that as I have no SDIO cards to do any measurements.

It depends entirely on the expense of accessing to DMA coherent memory
compared to accessing normal memory and then syncing it.

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