[PATCH] UBI: Decrease I/O count in ubi_scan

[Artem Bityutskiy]

On 07/21/2009 04:42 PM, Corentin Chary wrote:
> [   12.544598] NAND device: Manufacturer ID: 0xec, Chip ID: 0x36
> (Samsung NAND 64MiB 1,8V 8-bit)
> [   12.683697] Scanni
> [   12.691395] 0x000000000000-0x000000800000 : "Linux Kernel"
> [   12.699687] 0x000000800000-0x000002800000 : "Filesystem"
> [   12.707648] 0x000002800000-0x000004000000 : "Free"
> [   12.719948] UBI: attaching mtd2 to ubi0
> [   12.728005] UBI: physical eraseblock size:   16384 bytes (16 KiB)
> [   12.741397] UBI: logical eraseblock size:    15360 bytes
> [   12.751721] UBI: smallest flash I/O unit:    512
> [   12.760202] UBI: VID header offset:          512 (aligned 512)
> [   12.767589] UBI: data offset:                1024
> [   13.047943] UBI: attached mtd2 to ubi0
> [   13.055450] UBI: MTD device name:            "Free"
> [   13.063343] UBI: MTD device size:            24 MiB
> [   13.071539] UBI: number of good PEBs:        1536
> [   13.084148] UBI: number of bad PEBs:         0
> [   13.095572] UBI: max. allowed volumes:       89
> [   13.105468] UBI: wear-leveling threshold:    4096
> [   13.113178] UBI: number of internal volumes: 1
> [   13.129826] UBI: number of user volumes:     1
> [   13.140834] UBI: available PEBs:             0
> [   13.153634] UBI: total number of reserved PEBs: 1536
> [   13.160852] UBI: number of PEBs reserved for bad PEB handling: 15
> [   13.167731] UBI: max/mean erase counter: 2/1
> [   13.177809] UBI: image sequence number: 0

This flash does not look like something which could fit a 200MiB
volume.

>> And why do you presume is the improvement -
>> just less calls to MTD or really less I/O? Note MTD usually caches
>> the last read NAND page, so usually this is not about less I/O.
>
> In this case it seems vid and ec headers are not on the same page.

Strange. May be this is related to how they calculate ECC...
Or just a problem in the driver. Normally flashes like this would
have 256 byte sub-pages and have both headers in the same page.

Could you please check this? I just do not want to optimize it
for a bad/bogus driver. And I think now I recall that this patch
introduced slow down in some cases, when the driver can avoid reading
full page and calculatingfull ECC.

> So, if I understand things correctly, there *is* more I/O, and the same thing

Should not be more I/O.

> The same thing occurs with nandsim, because VID header offset is 2048,
> I don't know
> if it can happen on real flash.

With nandsim you should always have both headers on the same page, unless
you deliberately asked for the opposite by using -s option of ubiformat.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)