RE: JFFS3 & performance

Joakim Tjernlund
2004-12-16T14:45:12Z

> On Thu, 16 Dec 2004, Joakim Tjernlund wrote:
>
> > Hi List
> >
> > I am a long time JFFS2 user(and developer), but I haven't been following
> > JFFS2 for a year or two. I have noticed that JFFS3 has begun and I figured
> > I would offer a few thoughts.
> >
> > 1) Consider changing the start seed to crc32 from 0 to -1. Zero
> > is not a good start seed for crc32
> If you do point 2 this will not be needed :-)

Yes, but if you do point 2, you still have to consider start seed and it should
be != 0 regardless of what checksum you choose.

>
> >
> > 2) Consider another checksum algorithm. Crc32 is very expensive
> > and JFFS2 suffered severely in the early days. Now that crc32 is
> > very optimized that problem is less visible, but crc32 is still
> > expensive. Maybe an Adler32 checksum is good enough or a crc16?
> IMHO, NAND/ECC NOR are additionally protected by ECCs so that sounds
> reasonable. NORs are reliable, so that is reasonable too, IMHO.

Exactly.

>
> >
> > 3) Don't calculate a Adler32 checksum when comressing with zlib.
> > JFFS2 already has its own checksum.
> This is really seems reasonable. Personally I didn't do that, but guess it
> is possible to ask zlib not to add Adler32 checksums, right?

Yes, I tried this once but that was too long time ago for me to remember how
I did it. Currently JFFS2 skip the adler32 check upon read.
>
>
> I'll put your ideas to jffs3/TODO if you don't mind :-)

I don't mind :)

Jocke