linux-kernel - Re: [PATCH 00/10] AXFS: Advanced XIP filesystem

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Message-ID: <20080822183713.GC24179@shareable.org>
Date:	Fri, 22 Aug 2008 19:37:13 +0100
From:	Jamie Lokier <jamie@...reable.org>
To:	Jared Hulbert <jaredeh@...il.com>
Cc:	Greg Ungerer <gerg@...pgear.com>, Linux-kernel@...r.kernel.org,
	linux-embedded@...r.kernel.org,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	Jörn Engel <joern@...fs.org>,
	tim.bird@...sony.com, cotte@...ibm.com, nickpiggin@...oo.com.au
Subject: Re: [PATCH 00/10] AXFS: Advanced XIP filesystem

Jared Hulbert wrote:
> On Fri, Aug 22, 2008 at 11:13 AM, Jamie Lokier <jamie@...reable.org> wrote:
> > Greg Ungerer wrote:
> >> One thing for sure is that many people who do non-MMU setups
> >> are interested in XIP to get the space savings. These are very
> >> often small devices with very constrained RAM and flash. (For
> >> whatever it is worth single NOR flash only boards are common in
> >> these smaller form factors :-)
> >
> > I'm using XIP on a device with 32MB RAM.  The reason I use it is
> > _partly_ to save RAM, partly because programs start about 10 times
> > faster (reading NOR flash is slow and I keep the XIP region in RAM)
> 
> What kind of NOR you using?  That is not what I measure with fast
> synchronous burst NOR's.

I think the "fast" in "fast synchronous" gives it away :-)

I'm using Spansion MirrorBit S29GL128N, which reads at about 0.6 MByte/s.

Not because they're good, but because that's what the board I'm coding
for has on it.  I presume they were cheap and familiar to the board
designers.  (There is 32MB of RAM to play with after all.)

So start a sequence of Busybox processes from a shell script is noticable,
if it reads from NOR each time.

Oh, and it's a 166MHz ARM, so it's quite capable of decompressing
faster than the NOR can deliver.

-- Jamie
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