Re: open question on flash speed/app blocking

From: "Herman Oosthuysen" <Herman@WirelessNetworksInc.com>
To: "Cam Mayor" <cmayor@iders.ca>,
	"linux MTD mailing list" <linux-mtd@lists.infradead.org>
Subject: Re: open question on flash speed/app blocking
Date: Wed, 16 Jan 2002 12:47:57 -0700	[thread overview]
Message-ID: <000e01c19ec6$b2cd5980$0100007f@localdomain.wni.com.wirelessnetworksinc.com> (raw)
In-Reply-To: 02011512182209.16722@kilauea.iders.ca

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@WirelessNetworksInc.com
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@iders.ca>
To: linux MTD mailing list <linux-mtd@lists.infradead.org>
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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