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


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

On 2013-02-01 08:00, kyungsik.lee wrote:
On 2013-01-30 오전 6:09, Rajesh Pawar wrote:
Andrew Morton <akpm@...> wrote:

On Sat, 26 Jan 2013 14:50:43 +0900
Kyungsik Lee <kyungsik.lee@...> wrote:
[...]
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?
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?
BTW, what happened to the proposed LZO update - woudn't it better to merge
this first?

Also, under the hood LZ4 seems to be quite similar to LZO, so probably
LZO speed would also greatly benefit from unaligned access and some other
ARM optimisations
I didn't test with the proposed LZO update you mentioned. Sorry, which one do
you mean?
I did some tests with the latest LZO in the mainline.
In fact you can easily improve LZO decompression speed on armv7 by almost 50%
by adding just a few lines for enabling unaligend access:

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

Please see my other mail to LKML for details.

Cheers,
Markus

As a result, LZO is not faster in an unaligned access enabled on ARM. Actually
Slower.

Decompression time: 336ms(383ms, with unaligned access enabled)

You may refer to https://lkml.org/lkml/2012/10/7/85 to know more about it.

Thanks,
Kyungsik


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

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