jffs zlib tuning

[Mitch Bradley]

That might become moot if we switch from zlib to LZO for JFFS2, as has 
been discussed.


NoiseEHC wrote:
> This message is primarily written for Bernardo Innocenti but everybody 
> with relevant knowledge is welcomed to give some insight.
>
> I have decided two months ago that will write an asm implementation for 
> zlib inflate (decompression) since Mitch Bradley said that the read 
> speed is 3MB/sec which is dominated by the decompression code.
> http://lists.laptop.org/pipermail/devel/2007-November/007527.html
>
>
> Since then I went through the pain of installing linux in VirtualPC, 
> compiling the code in linux and ended up with a kernel module which can 
> test zlib code finally (took a month of my spare time, if I would have 
> known this in advance I would not have started...). Now I understand the 
> zlib code but need some info before acting on wrong assumptions:
>
> 1. Did anybody profile the kernel while reading files? Last thing I red 
> on this list is that the profiler does not work on the XO in kernel 
> mode. Did anybody fix that?
> 2. How does the file reading work? As I imagine the flash is read by DMA 
> and the resulting data is uncompressed to a buffer. Is it correct?. Is 
> the decompressed data gets copied to the target location or does it gets 
> decompressed to their final place? If it is copied, did somebody profile 
> how much time it takes? These questions are important to know how much 
> L2 cache is trashed in the process and which data needs prefetching.
> 3. How long is the average data length which jffs2 uses for calling inflate?
> 4. What is the average size of the length/distance code table?
> 4. Bernardo, as I imagine you are compiling kernels every day. If I send 
> you a "patch" (normally a rewritten inffast.c), would you test it on a 
> real XO machine, please?
>
> Thanks.
>
> _______________________________________________
> Devel mailing list
> Devel at lists.laptop.org
> http://lists.laptop.org/listinfo/devel
>