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SubjectRe: [RFC PATCH 0/4] Add support for LZ4-compressed kernels
On 2013-02-01 08:00, kyungsik.lee wrote:
> On 2013-01-30 오전 6:09, Rajesh Pawar wrote:
>>> Andrew Morton <akpm@linux-foundation.org> wrote:
>>>
>>> On Sat, 26 Jan 2013 14:50:43 +0900
>>> Kyungsik Lee <kyungsik.lee@lge.com> 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@oberhumer.com>, http://www.oberhumer.com/
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