[PATCH 11/16] lib: enable lzma decompression support for SPL build

[Weijie Gao]

On Thu, 2020-01-09 at 12:45 -0500, Tom Rini wrote:
> On Thu, Jan 09, 2020 at 04:10:12PM +0800, Weijie Gao wrote:
> > On Wed, 2020-01-08 at 08:22 +0100, Heinrich Schuchardt wrote:
> > > 
> > > On 1/8/20 4:01 AM, Weijie Gao wrote:
> > > > This patch enables LZMA decompression support for SPL build
> > > >
> > > > Signed-off-by: Weijie Gao <weijie.gao at mediatek.com>
> > > > ---
> > > >   lib/Kconfig  | 5 +++++
> > > >   lib/Makefile | 1 +
> > > >   2 files changed, 6 insertions(+)
> > > >
> > > > diff --git a/lib/Kconfig b/lib/Kconfig
> > > > index 965cf7bc03..2f38e37802 100644
> > > > --- a/lib/Kconfig
> > > > +++ b/lib/Kconfig
> > > > @@ -418,6 +418,11 @@ config SPL_LZ4
> > > >   	  fast compression and decompression speed. It belongs to the LZ77
> > > >   	  family of byte-oriented compression schemes.
> > > >
> > > > +config SPL_LZMA
> > > > +	bool "Enable LZMA decompression support for SPL build"
> > > > +	help
> > > > +	  This enables support for LZMA compression altorithm for SPL boot.
> > > 
> > > %s/altorithm/algorithm/g
> > > 
> > > Why do we need yet another algorithm for compression?
> > > 
> > > Doesn't Zstandard provide a much faster decompression?
> > > Cf. https://sites.google.com/site/powturbo/home/web-compression
> > > 
> > > Best regards
> > > 
> > > Heinrich
> > > 
> > > > +
> > > >   config SPL_LZO
> > > >   	bool "Enable LZO decompression support in SPL"
> > > >   	help
> > > > diff --git a/lib/Makefile b/lib/Makefile
> > > > index 1fb650cd90..8e51eec01c 100644
> > > > --- a/lib/Makefile
> > > > +++ b/lib/Makefile
> > > > @@ -64,6 +64,7 @@ obj-$(CONFIG_$(SPL_)ZLIB) += zlib/
> > > >   obj-$(CONFIG_$(SPL_)ZSTD) += zstd/
> > > >   obj-$(CONFIG_$(SPL_)GZIP) += gunzip.o
> > > >   obj-$(CONFIG_$(SPL_)LZO) += lzo/
> > > > +obj-$(CONFIG_$(SPL_)LZMA) += lzma/
> > > >   obj-$(CONFIG_$(SPL_)LZ4) += lz4_wrapper.o
> > > >
> > > >   obj-$(CONFIG_LIBAVB) += libavb/
> > > >
> > 
> > Hi Heinrich,
> > 
> > I need an algorithm with the maximum compression ratio to reduce the
> > size of the u-boot payload as much as possible.
> > 
> > I believe currently lzma and xz are the best choices.
> > Refer to:
> > https://catchchallenger.first-world.info/wiki/Quick_Benchmark:_Gzip_vs_Bzip2_vs_LZMA_vs_XZ_vs_LZ4_vs_LZO
> > 
> > Although they will take longer time for compression and decompression,
> > considering that the u-boot payload is usually small (<= 1MiB), there
> > will not be significant effect on decompression time.
> 
> Where does zstd fall in the list however?  Can you please try that and
> report back?  Thanks!
> 

My purpose is to reduce the size of u-boot binary, and my plan is to
compress the payload and the SPL decompress it at runtime.
I need smallest size here, not fastest decompression speed.

So there are two points must be taken into consideration:
the size of the decompressor (i.e. u-boot-spl.bin) and the size of the
compressed payload (u-boot.bin.gz/bz2/...).

Below is my test results, including all compression algorithms supported
by uImage, plus zstd:

Platform: mips - mt7628

Uncompressed size of u-boot.bin: 302736 (295KiB)

Commands for compression:
gzip -c -f -k -9
bzip2 -c -f -k -9
lzma -c -z -k -9
lzop -c -f -9
lz4 -f -9
zstd --ultra -f

Results:
algo. | spl.bin size  | compressed size | % of uncomp | total size
------------------------------------------------------------------------
gzip  | 26232 (25.6K) | 141207 (137KiB) | 46.64%      | 167439 (163KiB)
------------------------------------------------------------------------
bzip2 | 30616 (29.8K) | 135403 (132KiB) | 44.72%      | 166019 (162KiB)
------------------------------------------------------------------------
lzma  | 18920 (18.4K) | 112660 (110KiB) | 37.21%      | 131580 (128KiB)
------------------------------------------------------------------------
lzo   | 13288 (12.9K) | 152409 (148KiB) | 50.34%      | 165697 (161KiB)
------------------------------------------------------------------------
lz4   | 12408 (12.1K) | 167311 (163KiB) | 55.27%      | 179719 (175KiB)
------------------------------------------------------------------------
zstd  | 44824 (43.7K) | 149765 (146KiB) | 49.47%      | 194589 (190KiB)

As you can see lzma has the best compression ratio. The is the reason I
chose lzma here.

Best Regards