[RTEMS-gsoc2011] ISO9660 GSoC project report

Chris Johns chrisj at rtems.org
Fri Jul 8 00:30:00 UTC 2011

On 7/07/11 3:29 PM, Christophe Huriaux wrote:
>            My further work will firstly be dedicated to the improvement
>         of the
>         cache for this file-system. Since it's a read-only FS I plan to
>         implement a FIFO cache based on block access time : when a new
>         block has
>         to be put in the cache, the oldest (from an access time point of
>         view)
>         is uncached (the smallest entity in the ISO is called a sector
>         and is
>         2,048 bytes long). This method should help often accessed blocks
>         to stay
>         in the cache while the less accessed will be discarded. However,
>         I still
>         need some comments on this point since I'm not a cache manager
>         guru. :-)
>     How important is the need for an extra layer of cache over the
>     libblock cache ? A CDROM is not a fast device so caching is important.
>     The libblock cache will cache at the sector size if configured to do
>     so. The media block size for ATA(PI?) is 512 bytes how-ever the file
>     system layer can specify the file system block size to the libblock
>     cache.
>   I understand that adding others level of caching over libblock may not
> be beneficial to the filesystem performance, but what about the direct
> device I/O layer ? Should I rely on the underlying filesystem cache
> (which may or may not use libblock) in this case ?

I would not be to concerned about this at this point in time. If you see 
a performance issue later on you can take a look and determine what is 


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