Qt 5.3 Might Depend On SSE2 CPUs

[Jedibeeftrix]

Time to retire you Athlon XP ;-)

i have a friend still running his barton as a media centre on on ubuntu.

[gens]

speed, speed, and more speed..

cpu dispatching
google it

[darkcoder]

Or switch to a source based distro like Gentoo and compile your packages for your specific hardware like a gentleman.

Yes, while Gentoo well tuned can do miracles (I used it for a couple of years), some people try to use very old computers with the latest software. And you have to know when you need to move.

[gens]

SSE2 is the first generation of SIMD (Single Instruction Multiple Data) extensions giving ability to process two double precious floating point numbers at once, and more abilities to previous Integer only extension (MMX).

So what does this have to do with Qt 5? Well, they are using SSE2 (and higher versions if detected) on their 64bit releases, which accelerates their QML stuff. However on 32bit builds, all kind of SSE optimizations are turned off (By default). So this is going to be a pure win for modern CPU owners, who are running a 32bit OS.

Regards to the SSE3, it's going to give them ability to process 4 single precious floating point numbers (stored in one SIMD register) horizontally which wasn't possible (directly) in previous generations. This might be slower or faster depending on the hardware.

yes sse2 adds instructions to process 2 double precision floats, while sse1 was mainly used for four 32bit floats
sse2 ports the mmx integer instructions to xmm registers (mmx registers are 64bit while xmm are 128)
sse2 also adds nontemporal stores for xmm registers (write directly to ram, bypassing cache)

this is going to be a loss for 32bit OS people running QT things on sse2 capable cpus
at least for default compiled QT

sse3's horizontal things and couple new instructions are useful for some algorithms (boasted that its for DSP and 3D)
it all depends on how you need to process data and i doubt QT will need them (idk)


why disable it on builds ?
idk
cpu dispatching should be fine enough mechanism for one build to work good on all cpus
QT devs probably have their own reasons

[GreatEmerald]

You realize that more software than just KDE is using Qt?

You realise that there are distributions like Gentoo or ones dedicated to old hardware support? It's a default that can easily be changed.

[darkcoder]

Can anyone pls explain to me what kind of specific advantages it would bring supporting sse2 (or sse3) only cpus?

speed, speed, and more speed.

but even GLib these days have a codepath to use SSE2. No idea what the fuss, since don't remember people talking about it when glib introduced a similar approach.

http://upstream-tracker.org/changelo...changelog.html

If you have an old 2000-2003 computer you should either stop using new software and go back to Win 98/Linux 2.x based kernel distro, or get new hardware... plain and simple.

[DanL]

The whole article seems rubbish, it's like Michael was completely drunk. Half of the writing is nonsensical gibberish.

Speaking of drunkenness, it's been a while since we've had a good Phoronix beer article...

[curaga]

Oh and props to Qt for implementing charset conversions with SSE2, that's the first I hear them used for that. Even if it's been in Qt for three years now.

[curaga]

The whole article seems rubbish, it's like Michael was completely drunk. Half of the writing is nonsensical gibberish.

This. Dammit Michael, it's not even minor typos, it's like an ostrich shat on it, then put it in a blender.

[ninez]

Can anyone pls explain to me what kind of specific advantages it would bring supporting sse2 (or sse3) only cpus?

As others have pointed out- it's a compiler default, not "supporting sse2 (or sse3) only cpus"... And the advantage here is Hardware acceleration, which should lead to increased performance on operations where sse(X) is applicable. (floating point). So in Qt, it probably speeds up drawing operations, graphical processing - things like that. wikipedia on SSE; http://en.wikipedia.org/wiki/Streaming_SIMD_Extensions ... and http://en.wikipedia.org/wiki/SSE2 (the SSE2 article also has a paragraph on the differences between 'the slower x87 stack' and SSE2.