[U-Boot] [PATCH 0/8] JFFS2 fixes and performance improvements

[Mark Tomlinson]

These patches fix bugs and improve performance of JFFS2. Some of these
improvements can already be found in old mailing lists, but for some
reason they have not made their way into the u-boot source. I have the
feeling that any one of these patches didn't show enough performance gain
to warrant adding it to the source. I am hopeful that together, all these
patches can be seen to make a big difference.

One of these patches ("Only list each directory entry once") is a bug fix,
all the rest are for performance. Although performance is not high on the
priority list for a bootloader, the length of time it was taking to scan
a JFFS2 filesystem was painfully slow.

The code for mergesort was found in an abandoned u-boot patch, although I
have refactored the code somewhat. The original author is still shown at
the top of that file.

The timings below are with jffs2_summary_support turned off. With these
improvements, summary support was no longer useful - most of our time is
now spent loading the actual release. Even without this feature turned on,
the code will still load from a filesystem that has summary nodes.

Due to not having other resources, I also have not done anything for NAND
flash. At least some of these changes will be directly applicable to NAND
as well as NOR.

My own testing is on a system with a 1GHz PowerPC, and 256MB of NOR Flash.
The flash accesses are slow compared with processing power and RAM, so
minimising the number of flash accesses makes a huge difference. Here are
the timing comparisons for three JFFS2 operations on this system:
1) Scanning the file system
2) Getting a director listing of the top level, and
3) Loading a 30MB file.

Times are in seconds, and the contribution from each patch has been
measured:

                         Scan    List    Load    Total
Original:               266.0    17.3    23.4   306.7
Speed up comparison:     52.3    17.3    23.4    93.0
List dir entries once:   52.3    11.0    23.4    86.7
Improve read speed:      52.3     0.8     5.4    58.5
Optimize building lists: 31.9     0.8     5.4    38.1
Change scansize:         30.8     0.8     5.4    37.0
Use cleanmarker:         16.0     0.8     5.4    22.2
Use mergesort:            2.0     0.8     5.4     8.2

Note that "List dir entries once" is not a speed improvement as such, but
because old versions of a file and deleted files are no longer scanned,
there is an improvement on this filesystem (the flash is approx half full).

Also, "change scansize" appears to do very little in this benchmark list.
But without it, the "use cleanmarker" would not show as much improvement.


Mark Tomlinson (8):
  JFFS2: Return early when file read not necessary
  JFFS2: Speed up and fix comparison functions
  JFFS2: Only list each directory entry once
  JFFS2: Improve speed reading flash files
  JFFS2: Optimize building lists during scan
  JFFS2: Change scansize to match linux kernel
  JFFS2: Use CLEANMARKER to reduce scanning time
  JFFS2: Use merge sort when parsing filesystem

 fs/jffs2/Makefile        |   1 +
 fs/jffs2/jffs2_1pass.c   | 245 +++++++++++++++++++++++++++++------------------
 fs/jffs2/jffs2_private.h |   4 +
 fs/jffs2/mergesort.c     |  70 ++++++++++++++
 4 files changed, 228 insertions(+), 92 deletions(-)
 create mode 100644 fs/jffs2/mergesort.c

-- 
1.9.1