Re: [RFC PATCH v2 0/4] Add support for LZ4-compressed kernel

Nicolas Pitre
2013-02-26T20:59:59Z

On Tue, 26 Feb 2013, Markus F.X.J. Oberhumer wrote:

> On 2013-02-26 07:24, Kyungsik Lee wrote:
> > Hi,
> >
> > [...]
> >
> > Through the benchmark, it was found that -Os Compiler flag for
> > decompress.o brought better decompression performance in most of cases
> > (ex, different compiler and hardware spec.) in ARM architecture.
> >
> > Lastly, CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is not always the best
> > option even though it is supported. The decompression speed can be
> > slightly slower in some cases.
> >
> > This patchset is based on 3.8.
> >
> > Any comments are appreciated.
>
> Did you actually *try* the new LZO version and the patch (which is attached
> once again) as explained in https://lkml.org/lkml/2013/2/3/367 ?
>
> Because the new LZO version is faster than LZ4 in my testing, at least
> when comparing apples with apples and enabling unaligned access in
> BOTH versions:
>
> armv7 (Cortex-A9), Linaro gcc-4.6 -O3, Silesia test corpus, 256 kB block-size:
>
> compression speed decompression speed
>
> LZO-2012 : 44 MB/sec 117 MB/sec no unaligned access
> LZO-2013-UA : 47 MB/sec 167 MB/sec Unaligned Access
> LZ4 r88 UA : 46 MB/sec 154 MB/sec Unaligned Access

To be fair, you should also take into account the compressed size of a
typical ARM kernel. Sometimes a slightly slower decompressor may be
faster overall if the compressed image to work on is smaller.

Nicolas