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

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Date:	Mon, 15 Sep 2008 17:40:12 +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:
> > I think the "fast" in "fast synchronous" gives it away :-)
> 
> Yes, I suppose it does.
> 
> > I'm using Spansion MirrorBit S29GL128N, which reads at about 0.6 MByte/s.
> 
> I think you should get more like an order of magnitude higher.... Get
> an expert to look at your timings in the bootloader.  Make sure things
> are cached too.  ioremap_cached()...

Yes, looking at the Spansion datasheet, if it were interfaced properly
it should be quite fast.  (25ns access time for in-page 16-bit reads,
100ns for random reads).

I'll see if ioremap_cached() makes a difference to streaming read
performance.

The BSP suppliers have been quite cautious in places, flushing cache a
bit too often.  (I'm not surprised - we had disk ext3 filesystem
corruption due to insufficient cache flushing in places too.)

> > Oh, and it's a 166MHz ARM, so it's quite capable of decompressing
> > faster than the NOR can deliver.
> 
> Depends on how you are measuring it.   You ought to be able to get at
> least 2 orders of magnitude higher read speeds with a good sync Flash.
>  Some of the newer stuff is even faster.

Thanks.

Oh, how I look forward to the day of working with current kernels and
current hardware.

-- Jamie

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