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


Markus F.X.J. Oberhumer <markus@...>
 

On 2013-01-30 11:23, Johannes Stezenbach wrote:
On Mon, Jan 28, 2013 at 11:29:14PM -0500, Nicolas Pitre wrote:
On Mon, 28 Jan 2013, Andrew Morton wrote:

On Sat, 26 Jan 2013 14:50:43 +0900
Kyungsik Lee <kyungsik.lee@...> wrote:

This patchset is for supporting LZ4 compressed kernel and initial ramdisk on
the x86 and ARM architectures.

According to http://code.google.com/p/lz4/, LZ4 is a very fast lossless
compression algorithm and also features an extremely fast decoder.

Kernel Decompression APIs are based on implementation by Yann Collet
(http://code.google.com/p/lz4/source/checkout).
De/compression Tools are also provided from the site above.

The initial test result on ARM(v7) based board shows that the size of kernel
with LZ4 compressed is 8% bigger than LZO compressed but the decompressing
speed is faster(especially under the enabled unaligned memory access).

Test: 3.4 based kernel built with many modules
Uncompressed kernel size: 13MB
lzo: 6.3MB, 301ms
lz4: 6.8MB, 251ms(167ms, with enabled unaligned memory access)
What's this "with enabled unaligned memory access" thing? You mean "if
the arch supports CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS"? If so,
that's only x86, which isn't really in the target market for this
patch, yes?
I'm guessing this is referring to commit 5010192d5a.

It's a lot of code for a 50ms boot-time improvement. Does anyone have
any opinions on whether or not the benefits are worth the cost?
Well, we used to have only one compressed format. Now we have nearly
half a dozen, with the same worthiness issue between themselves.
Either we keep it very simple, or we make it very flexible. The former
would argue in favor of removing some of the existing formats, the later
would let this new format in.
This reminded me to check the status of the lzo update and it
seems it got lost?
http://lkml.org/lkml/2012/10/3/144
The proposed LZO update currently lives in the linux-next tree.

I had tried several times during the last 12 months to provide an update
of the kernel LZO version, but community interest seemed low and I
basically got no feedback about performance improvements - which made
we wonder if people actually care.

At least akpm did approve the LZO update for inclusion into 3.7, but the code
still has not been merged into the main tree.
> On 2012-10-09 21:26, Andrew Morton wrote:
> [...]
> The changes look OK to me. Please ask Stephen to include the tree in
> linux-next, for a 3.7 merge.

Well, this probably means I have done a rather poor marketing. Anyway, as
people seem to love *synthetic* benchmarks I'm finally posting some timings
(including a brand new ARM unaligned version - this is just a quick hack which
probably still can get optimized further).

Hopefully publishing these numbers will help arousing more interest. :-)

Cheers,
Markus


x86_64 (Sandy Bridge), gcc-4.6 -O3, Silesia test corpus, 256 kB block-size:

compression speed decompression speed

LZO-2005 : 150 MB/sec 468 MB/sec
LZO-2012 : 434 MB/sec 1210 MB/sec

i386 (Sandy Bridge), gcc-4.6 -O3, Silesia test corpus, 256 kB block-size:

compression speed decompression speed

LZO-2005 : 143 MB/sec 409 MB/sec
LZO-2012 : 372 MB/sec 1121 MB/sec

armv7 (Cortex-A9), Linaro gcc-4.6 -O3, Silesia test corpus, 256 kB block-size:

compression speed decompression speed

LZO-2005 : 27 MB/sec 84 MB/sec
LZO-2012 : 44 MB/sec 117 MB/sec
LZO-2013-UA : 47 MB/sec 167 MB/sec

Legend:

LZO-2005 : LZO version in current 3.8 rc6 kernel (which is based on
the LZO 2.02 release from 2005)
LZO-2012 : updated LZO version available in linux-next
LZO-2013-UA : updated LZO version available in linux-next plus
ARM Unaligned Access patch (attached below)


(Cc: added, I hope Markus still cares and someone could
eventually take his patch once he resends it.)

Johannes
--
Markus Oberhumer, <markus@...>, http://www.oberhumer.com/

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