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List:       yaffs
Subject:    Re: [Yaffs] some questions
From:       Charles Manning <manningc2 () actrix ! gen ! nz>
Date:       2011-08-21 18:08:27
Message-ID: 201108220608.27980.manningc2 () actrix ! gen ! nz
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On Saturday 20 August 2011 11:38:22 srimugunthan dhandapani wrote:
> Hi all,
> I have a few questions about yaffs2. Thanks in advance for replying.


I Suggest you read HowYaffsWorks.pdf. It is on yaffs.net.

> 1. Yaffs2 now ensures that pages within a block will be written
> sequentially. With multiple threads is it possible that pages within a
> block may be written out of order?
No

> 2. Ext4 is supposed to better in multithreaded performance in
> comparison to yaffs2 in Android.
>    What sorts of problems have to solved in yaffs2 for better
> multi-threaded performance?.
At this stage yaffs is still single threaded locked but there has been some 
work moving towards multi-threading.
>    How can one contribute toward this effort?
> 3. Is it possible to get reasonably accurate runtime memory
> consumption from checkpoint size,
Not really.
> 	 What is the approximate relationship between checkpoint size and
> runtime mem consumption
> 	 is there a linear relationship like,
> 	Checkpointsize + ShortOpCacheSize + YAffs tempbuffers + (?) = Runtime
> memory consumption
There is a relationship. Have a read of HowYaffsWorks first. That will help 
start the understanding.

> 4. I want to take yaffs2 benchmark measurements on an aged
> filesystem(ie which has been used for quite some months).
>    Any ideas for how to artificially create such an yaffs2 image?.

The easiest thing to do here is probably to use the simulator.

I will be very interested in what you find. I would be surprised if a long 
lifetime creates and degradation. Fragmentation is a problem on mechanical 
storage because this forces the disk to perform lots of seeks to read a file. 
This does not hurt flash because there is no seek time.


>    I want something like, if i create 100MB aged yaffs2 image , is
> there a way  i can write it like multiple times to create a larger,
> say 1GB image?
Not really because duplicating tags and sequence Ids will not work.

-- Charles\



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