[U-Boot] [PATCH,V2] JFFS2: accelerate scanning.

[Detlev Zundel]

Hi Baidu,

> Hi,Detlev :
>
> 2011/4/19 Detlev Zundel <dzu at denx.de>:
>> Hi Baidu,
>>
>>>  Syncs up with jffs2 in the linux kernel:
>>>  1/ Change DEFAULT_EMPTY_SCAN_SIZE from 4KB to 256 Bytes.
>>>  2/ If the 1KB data is 0xFF after the cleanmarker, skip
>>>  and scan the next sector.
>>>  3/ Change the buffer size from 4KB to 128KB which is the
>>>  common size of erase block.
>>
>> There is no "common size of erase block".  Looking into the Linux code,
>> it uses "max(erase block size, 128k)" for its buffer to speed up reading
>> from NAND and the 128k seem to be a kmalloc limit.
>>
>> So maybe a "increase buffer size from 4KiB to 128KiB to reduce number of
>> read operations" would be more fitting.  By the way, does this change
>> contribute to the performance increase at all, or is the increase simply
>> due to DEFAULT_EMPTY_SCAN_SIZE?
>>
>
> Yes, I think it is useful to speed up the scanning.

Don't get me wrong, but I was not asking whether you "think" it speeds
up the scanning.  When it comes to performance, I learnt to trust
numbers olnly.  This may in part be because I myself occassionally was
completely wrong in predicting performance issues.

So I am still eager to see actual numbers if this _really_ speeds up
scanning.

Cheers
  Detlev

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