open question on flash speed/app blocking

Vipin Malik vipin.malik at
Wed Jan 16 16:18:46 EST 2002


I've also done quite a bit of blocking time tests on JFFS2 (about 6-8 months
ago). See the (JFFS) list archives for details and graphs etc.


Herman Oosthuysen wrote:

> Hmm, the problem is not writing to flash per se, but rather garbage
> collection, which requires the erase of dirty Flash sectors.  Erasing a
> sector on an Intel chip can take from a couple hundred milliseconds to about
> 15 seconds, depending on the age of the device - by the time a chip gets to
> 15 seconds, I usually toss them away.  Flash chips tend to get slower with
> age.  So, you have to repeat your tests a few hundred thousand times before
> you can draw any real conclusions.  This also means that the worst case
> performance will be about the same, irrespective of the file system used,
> since the hardware constraints will eventually dominate.
> If your system has to write to flash every few seconds, then consider using
> a file system that has a large write cache, to enable you to survive the
> periods when the system is busy erasing a sector.
> --
> Herman Oosthuysen
> Herman at
> Suite 300, #3016, 5th Ave NE,
> Calgary, Alberta, T2A 6K4, Canada
> Phone: (403) 569-5688, Fax: (403) 235-3965
> ----- Original Message -----
> From: Cam Mayor <cmayor at>
> To: linux MTD mailing list <linux-mtd at>
> Sent: Tuesday, January 15, 2002 11:18 AM
> Subject: open question on flash speed/app blocking
> Hi all,
> We're making an app that periodically writes a persistance file to flash.  I
> haven't actually gotten a flash file system area working yet on my board, so
> i can't test this yet for speed.   I know that the results will vary with
> the
> hardware, the filesystem used, and a handful of other factors.  I'm assuming
> that a write to the flash will be blocking - that is, nothing else will be
> allowed to happen on the bus while that function is being performed.
> For a file the size of 32bytes, 1kByte, and 32kBtyes, what kind of blocking
> delay might one expect from linux writing to flash for each of those file
> sizes?  What would be an optimum flash filesystem to use for something like
> this?  (if there is one)
> cheers,
> cam
> ps. i'm using linux 2.4.6-rmk1-rayl1 and 2.4.16-rmk2.  I could use the
> latest
> kernel, too, i just haven't gotten around to it.  For development purposes,
> i'm using a cirrus CDB89712 development board, which has the cs89712
> processor and some Intel 28f320B3 flash on it.
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