execute-in-place with Ext2

mcortese — Mon, 08 Sep 2008 17:37:32 +0000

Is execute-in-place applied to ext2 worth investigating with latest notebooks that feature solid state devices as the main storage (e.g. the Asus EeePC)?

Why XIP doesn't get so much use with Linux...

HalfMoon — Fri, 05 Sep 2008 00:10:47 +0000

XIP is less interesting now than it was a few years back. The thing is that it basically applies only to NOR flash ... but it's NAND which is getting the huge price shrinkage. I suppose folk developing ROM images could also use XIP, but that just seems to emphasize the point that the audience here doesn't seem to be one with long term growth.

A technical reason why XIP isn't as interesting lately include that the access times hurt ... it's pretty much always a lot faster to run from RAM. So you don't want XIP for frequently-used code.

There are places where XIP matters a lot, though many of them don't run Linux. Some won't even run uClinux. Any place you see microcontrollers in use, it's likely you're talking about System-On-Chip processors with integrated flash used for program memory. Things like AVR8 (and some AVR32), MSP430, PIC (sigh), ARM7TDMI, C2000 ... where 256KBytes of flash is a rather large part, as is 32KB of RAM, and a 60 MHz clock rate is pretty fast.

XIP with uClinux can be a way to keep system costs low though. If you're using only a 4 MB flash, and 16 MB of RAM, you're probably pretty close to the performance edge. Getting a few extra MBytes of working memory by using XIP can help shave dollars from your BOM.

LWN: Comments on "AXFS: a compressed, execute-in-place filesystem"

execute-in-place with Ext2

Why XIP doesn't get so much use with Linux...