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Massimo B.
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PostPosted: Mon May 21, 2012 10:40 am    Post subject: libjpeg-turbo on PPC Reply with quote

Code:
Title: The default JPEG implementation
Author: Samuli Suominen <ssuominen@gentoo.org>
Content-Type: text/plain
Posted: 2012-04-24
Revision: 1
News-Item-Format: 1.0
Display-If-Installed: =media-libs/jpeg-8*

libjpeg-turbo is a derivative of libjpeg that uses MMX, SSE, SSE2,
and NEON SIMD instructions to accelerate baseline JPEG
compression/decompression by about 2-4x on amd64, arm and x86
platforms. It is based on libjpeg/SIMD but has numerous enhancements.

All users are recommended to migrate:

# emerge --deselect media-libs/jpeg
# emerge --oneshot media-libs/libjpeg-turbo

media-libs/jpeg:0 will be left in tree as a fallback implementation.

What does that mean for us? The only sentence about PPC I could found in the web was:
Quote:
libjpeg-turbo works on powerpc, but doesn't get any speedup over regular libjpeg.
Is that still correct?
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blob999
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PostPosted: Mon May 21, 2012 1:57 pm    Post subject: Reply with quote

that's right, there isn't any optimization for powerpc or altivec simd.
Jpeg optimizations with AltiVec exists only on macosx for powerpc.
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Massimo B.
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PostPosted: Mon May 21, 2012 2:09 pm    Post subject: Reply with quote

Too bad again.. I would love to see some improvements on ppc too, but the arch is dying. Then most altivec optimizations such as glibc are only on MacOSX, can't we just use those :) ?

So migrating to libjpeg-turbo is advised on ppc too, even without performance gain?
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PostPosted: Mon May 21, 2012 3:43 pm    Post subject: Reply with quote

migrating to libjpeg-turbo is indifferent for ppc users...

As quite abandoned platform (at least for desktop users) there also are fewer free developers equipped with these machines...
You could try "a reverse reading" of this manual:
http://developer.apple.com/legacy/mac/library/documentation/Performance/Conceptual/Accelerate_sse_migration/Accelerate_sse_migration.pdf
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PostPosted: Fri May 25, 2012 9:14 pm    Post subject: Re: libjpeg-turbo on PPC Reply with quote

Massimo B. wrote:

What does that mean for us? The only sentence about PPC I could found in the web was:
Quote:
libjpeg-turbo works on powerpc, but doesn't get any speedup over regular libjpeg.
Is that still correct?

Where did you find this statement? In any case, it does not matter :) You can easily run some jpeg decoding benchmarks with any image yourself. For example, on my playstation3 (with CFLAGS="-g -mcpu=cell -mtune=cell -maltivec -O2 -fomit-frame-pointer -pipe"):
Code:
# wget http://www.nasa.gov/images/content/618486main_earth_full.jpg

# emerge media-libs/jpeg-8d
# time djpeg 618486main_earth_full.jpg > /dev/null

real   0m5.298s
user   0m5.200s
sys   0m0.098s

# emerge ="media-libs/libjpeg-turbo-1.2.0-r1"
# time djpeg 618486main_earth_full.jpg > /dev/null

real   0m4.193s
user   0m4.096s
sys   0m0.095s

Yes, libjpeg-turbo clearly can't be 2-4x times faster on PPC without altivec optimizations. But it still has some non-SIMD performance optimizations too (primarily huffman), which should give it some advantage on any platform.
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Massimo B.
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PostPosted: Tue May 29, 2012 11:59 am    Post subject: Reply with quote

Thank you.
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