[RFC] slight UBI scan time improvement

[Hamish Moffatt]

On Wed, Apr 23, 2008 at 11:21:04AM +0300, Artem Bityutskiy wrote:
> Hi,
> 
> On Wed, 2008-04-23 at 10:13 +0200, Matthieu CASTET wrote:
> > > [    0.950000] NAND device: Manufacturer ID: 0xec, Chip ID: 0xdc (Samsung NAND 512MiB 3,3V 8-bit)
> > > [    0.960000] Scanning device for bad blocks
> > > [    1.000000] Bad eraseblock 494 at 0x03dc0000
> > > [    1.050000] Bad eraseblock 1300 at 0x0a280000
> > > [    1.140000] Bad eraseblock 2554 at 0x13f40000
> > > [    1.160000] Bad eraseblock 2923 at 0x16d60000
> > > [    1.200000] Bad eraseblock 3349 at 0x1a2a0000
> > > [    1.230000] Bad eraseblock 3790 at 0x1d9c0000
> > > [    6.890000] UBI: attached mtd9 to ubi0
> > > 
> > > 
> > > 
> > > Hamish
> > 
> > Do you know when the bad block scanning finish and the ubi scan start ?
> 
> Good point Matthieu. Indeed, _at least_ 1.23 sec is spend in the driver
> for scanning against bad eraseblocks to build in-memory bad block table
> (BBT). And it is probably more than 1.23 sec. If you start using
> on-flash bad block table, this should go away. I never used on-flash
> BBT, but I know MTD supports this and for example OLPC has on-flash BBT.

Well I think from past use of "time ubiattach ..." that most of
the missing time is in the attach. 

I've added a message at start of ubi_attach_mtd_dev(), but I can't test it 
from home as I left my test hardware at the office switched off tonight..
I'll confirm tomorrow.

Would combining the bad block scan with the UBI scan save time? I guess
it would be a bad layering violation however :-)


What sort of speed do you get using
dd if=/dev/mtdblock9 of=/tmp/foo bs=128K count=64
(where mtdblock9 is your raw mtd NAND device). I'm seeing about 6
seconds to read that 8Mb, which is quite long I guess.

Hamish
-- 
Hamish Moffatt VK3SB <hamish at debian.org> <hamish at cloud.net.au>