Is a 12 MB/s microSD overkill for what the glamo driver does?

Jim Colton jimcolt at
Thu Jul 31 15:07:12 CEST 2008

Oh, I see.  Good thought about flushing cache.

The speeds for read and write are different on a SD card with read being
always faster and so I was thinking to do only the read test and to have
dd(1) read directly from the device rather than going through the file
system - taking the file system code out of the picture since time due to it
is a constant factor.
The size of the read buffer won't matter since what was read is given to
/dev/null.  The speed and buffering of the underlying Glamo driver and SD
card will be the only player - which is what I am testing.

I'll use something like:

time dd if=/dev/mm<whatever the SD device name is> count=512000 bs=1024

..and dividing the value for System time into (512000 * 1024) for the

On Wed, Jul 30, 2008 at 11:07 PM, Mike Montour <mail at> wrote:

> Jim Colton wrote:
> > Hi Mike,
> >
> > I looked at the code your wrote.  It doesn't do anything that 'time dd'
> > already can do.
> It includes an fsync() in the timing measurement when writing the file,
> and does a posix_fadvise() before reading it back (both intended to make
> sure that the I/O is going to the device under test rather than just
> hitting cache memory). You can do the same things in a 'dd'-based test,
> but it requires a few additional steps.
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