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

[Corentin Chary <corentin.chary@gmail.com>]

On Tue, Jul 21, 2009 at 4:15 PM, Artem Bityutskiy<dedekind1@gmail.com> wrote:
> 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.

After reading more code, when HW ECC is enabled, atmel_nand only
handle full page write.


A last question, to be sure,
If we use something like (Samsung K9F2G08UQM) we have writesize = 2048
and subpage = 512.
VID header offset will be 512.
ec_hdr is in the first subpage
vid_hdr is in the second subpage

So, there will two I/O (two subpage read) ?
Reading nand_base.c I believe that the cache is only used when subpage
read is not possible.

Thanks for your time,

-- 
Corentin Chary
http://xf.iksaif.net - http://uffs.org