CPU caching of flash regions.

Alex Lennon ajlennon at arcom.co.uk
Tue May 15 06:46:10 EDT 2001


> Actually, the board used for the offending profile is a board with paged
> access to the flash, so it's slightly slower than some others - but the
> overhead shouldn't be too high. And the cache benefit would be more

> What kind of chip is being used?

Two contiguous Intel Strataflash 28F640's giving 16Mb total

> What bus is it on?


> And how fast is it?


> Second. What kind of processor, and what kind of chipset are being used?

National Geode GX1 300Mhz with CS5530 support chipset

To generate some figures I knocked together code which reads the 16Mb from
the flash, paging as it goes. Nothing is done with the data. This takes
about 16s

With the hardcoded value of CONFIG_JFFS2_FS_DEBUG set to 2 in
I get jffs2 root fs mount times in excess of 34s.

When I remove the debugging I get mount times of around 26s

Obviously the figures obtained from df need some massaging to take account
of compression
but I get:

/dev/root                14336      3760     10576  26% 	/
/dev/mtdblock1            1280       644       636  50% 	/var
/dev/ram0                 3963        26      3733   1% 		/var/tmp

So what does this mean ? Can I expect a fourfold increase in mount time with
a full f/s ?
Should I be comparing a 26s jffs2 mount to an idealistic 4s 4Mb flash read ?



More information about the linux-mtd mailing list