linux-kernel - Re: [RFC] LZO de/compression support

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Date:	Mon, 28 May 2007 15:53:41 -0700
From:	"Bret Towe" <magnade@...il.com>
To:	"Nitin Gupta" <nitingupta910@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>, linux-mm-cc@...top.org,
	linuxcompressed-devel@...ts.sourceforge.net,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Daniel Hazelton" <dhazelton@...er.net>,
	"Richard Purdie" <richard@...nedhand.com>,
	"Satyam Sharma" <satyam.sharma@...il.com>
Subject: Re: [RFC] LZO de/compression support - take 6

On 5/28/07, Nitin Gupta <nitingupta910@...il.com> wrote:
> Hi,
>
> This is kernel port of LZO1X-1 compressor and LZO1X decompressor (safe
> version only).
>
> * Changes since 'take 5' (Full Changelog after this):
> - Added compressor and decomrpesssor as separate and hidden config
> options (default: n)
> - Cleanups: removed LZO_CHECK_MPOS_NON_DET macro
> - removed PTR* macros.
>
> * Benchmarks: (system: P4 3GHz, 1G RAM)
> (Using tester program from Daniel)
>
> Following compares this kernel port ('take 6') vs original miniLZO code:
>
> 'TinyLZO' refers to this kernel port.
>
> 10000 run averages:
> 'Tiny LZO':
>        Combined: 61.2223 usec
>        Compression: 41.8412 usec
>        Decompression: 19.3811 usec
> 'miniLZO':
>        Combined: 66.0444 usec
>        Compression: 46.6323 usec
>        Decompression: 19.4121 usec
>
> Result:
> Overall: TinyLZO is 7.3% faster
> Compressor: TinyLZO is 10.2% faster
> Decompressor: TinyLZO is 0.15% faster
>
> TODO: test 'take 6' port on archs other than x86(_32)
>
> * Changelog vs. original LZO:
> 1) Used standard/kernel defined data types: (this eliminated _huge_
> #ifdef chunks)
>   lzo_bytep -> unsigned char *
>   lzo_uint -> size_t
>   lzo_xint -> size_t
>   lzo_uint32p -> u32 *
>   lzo_uintptr_t  -> unsigned long
> 2) Removed everything #ifdef'ed under COPY_DICT (this is not set for
> LZO1X, so removed corres. parts).
> 3) Removed code #ifdef'ed for LZO1Y, LZO1Z, other variants.
> 4) Reformatted the code to match general kernel style.
> 5) The only code change: (as suggested by Andrey)
> -#if defined(__LITTLE_ENDIAN)
> -                             m_pos = op - 1;
> -                             m_pos -= (*(const unsigned short *)ip) >> 2;
> -#else
> -                             m_pos = op - 1;
> -                             m_pos -= (ip[0] >> 2) + (ip[1] << 6);
> -#endif
>
> + m_pos = op - 1 - (cpu_to_le16(*(const u16 *)ip) >> 2);
>
> (Andrey suggested le16_to_cpu for above but I think it should be cpu_to_le16).
> *** Need testing on big endian machine ***
>
> Similarly:
> -#if defined(__LITTLE_ENDIAN)
> -                             m_pos -= (*(const unsigned short *)ip) >> 2;
> -#else
> -                             m_pos -= (ip[0] >> 2) + (ip[1] << 6);
> -#endif
>
> + m_pos -= cpu_to_le16(*(const u16 *)ip) >> 2;
>
> 6) Get rid of LZO_CHECK_MPOS_NON_DET macro and PTR* macros.
>
>
> I think it's now ready for mainline inclusion.
>
>
>  include/linux/lzo1x.h        |   66 +++++++++++
>  lib/Kconfig                  |    6 +
>  lib/Makefile                 |    2 +
>  lib/lzo1x/Makefile           |    2 +
>  lib/lzo1x/lzo1x_compress.c   |  259

tested this on ppc and its still good
is there any reason to bother with a test on amd64?
if there is I might be able to get to it tonight
-
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