Amiga.org
Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: jahc on March 02, 2003, 03:23:20 AM
-
Does anyone know how much faster altivec enabled programs are on a G4, than non-altivec programs? Like, 40% faster or what?
-
not sure how much faster it is, but im pretty sure that with the right software it is quite a bit faster
perhaps you can get some info on the speed differences from apple.com
im not a big fan of SIMD technology, it really does not appeal to me
-
The long and short answer is:
It depends.
If the app can benefit from SIMD capabilities, it will get a 400% boost for the areas where SIMD is useful.
It the app cannot benefit from SIMD, you won't see a single bit of better performance.
Most apps have segments that would benefit from SIMD, others that would find it useless. So, the long and short of it is, it depends on how many areas in the application will benefit from the SIMD capabilities of Altivec.
-
by jahc on 2003/3/1 21:23:20
Does anyone know how much faster altivec enabled programs are on a G4, than non-altivec programs? Like, 40% faster or what?
Lightwave raytrace test is 15% faster on G4 vs a G3 of the same speed, that should be mostly an Altivec delta.
-Tig
-
> im not a big fan of SIMD technology, it really does not appeal to me
Why? The principle seems quite useful to me.
Kay
-
Are you sure that just isn't floating point code running faster on the G4?
-
by Hattig on 2003/3/1 22:55:08
Are you sure that just isn't floating point code running faster on the G4?
Why are you thinking that??? With both parts running at the same speed, I dont think the FPU should be running at different speeds.
-Tig
-
G4/G3 comparison:
According to benchmark tests performed on Mac hardware the G3/G4's integer performances (does not utilize Altivec) is basically the same at similar clock speeds.
However the floating point performance is roughly 30% better at the same clock speeds for the G4. (And of course there are often huge additional performance gains for Altivec optimised software.)
Some official data from Motorola and IBM for some rough comparison:
------CPU----------------------------Spec95 (int)-Spec95 (fp)
-------------------------------------------------------------------------
G3 750FX @ 900 MHz--------------39.9 ---------21.1-------
G4 7451 @ 733 MHz----------------32.1 ---------23.9-------
The integer performance difference is about what you would expect, based on the higher G3 clock rate. Yet still the G4 is about 12% faster with regard to floating point performance.
My conclusion, even when taking out of account the very cool Velocity Engine, the G4 is a slightly better overall performing CPU than a G3 at the same clock rate.
Regarding the Velocity Engine (the G3 has none), AltiVec adds 128-bit-wide vector execution units to the PowerPC architecture. Here (http://developer.apple.com/hardware/ve/summary.html) you can find a well done introduction. The amount of performance gains differ greatly between different types of applications and how well they are optimised to use Altivec's benefits. Recent MacOS versions of Adobe Photoshop are well known for being well optimised for this Velocity Egine, and here (http://www.xlr8yourmac.com/G4ZONE/photoshop_1GHzPCvsG4.html) you can find some interesting (non-Apple Computer, Inc) benchmark comparisons.
-
Anywhere from 1x to 16x performance. It really depends.
More things can be accelerated for AltiVec than other 'SIMD' units since it has a more complete instruction set. Also it has the permute operator which is useful in various non-SIMD operations.
The most important factor is, of course, the ability of the programmer. :-D
-
Anywhere from 1x to 16x performance. It really depends.
More things can be accelerated for AltiVec than other 'SIMD' units since it has a more complete instruction set. Also it has the permute operator which is useful in various non-SIMD operations.
Yes, I remember Altivec was once described as MMX done right! It's not appropiate for some things but very useful for others, any DSP (read FFT or wavelet) algorithum is going to get a massive boost from Altivec. So If you are into audio or video processing you are going to be very happy.
Unfortunately the G4 has a now aging bus structure which means the Altivec is going to be starved for data, the PPC970 should fix this and Altivec will get to show it's true colours.
The most important factor is, of course, the ability of the programmer.
Intels' Floating point numbers are pretty respectable these days and this is largly due to them using the SSE2 unit to do floating point calculations. There is a clever trick called auto-vectorisation which can find simple segments of code that can be converted to SSE instructions and since the SSE unit is much better than the standard x86 FPU it gets much better numbers.
Apple are doing a lot of work on GCC so I imagine they are putting something similar in. That means any PPC OS can benefit from it. Anything even vaguly complex however is best done by hand.
BTW anyone know who did Altivec?
Most seem to assume it's a Motorola thing but thats not the case. It was a joint project between IBM Motorola and Apple. Apple did the Architecture.
-
It does not have to run at different speed to be faster..
It might be more efficient. You know MHz is realy not the only thing that tells how fast something is. You must also think about the IPC. MHz is only a good mesurment if you compare 2 cpus with the exactly same core :-P
-
minator wrote:
BTW anyone know who did Altivec?
Most seem to assume it's a Motorola thing but thats not the case. It was a joint project between IBM Motorola and Apple. Apple did the Architecture.
BTW did you know you are completely wrong??? Though the PPC is an effort from all 3, though it draws strongly on IBM Power Architecture, all by themselves Motorola did Altivec. Altivec of course led to the slow down in the PPC line and Intel passing them. The great split between IBM & Motorola was all about Altivec, and until Apple and Motorola paid IBM to make 500 Mhz G4's, (because Motorola was throwing out more dies then they could keep) IBM didnt make any Altivec parts. In addition since Motorola owned Altivec, IBM couldnt sell faster Altivec parts then Motorola, another bottleneck as Motorola did not spend sufficient resources to keep up with anyone in this regard. IBM's 970 will be the first real effort by IBM at an Altivec aware PPC, its liable to remove Motorola PPC parts from all Apple products (if Apple doesnt go AMD as is rumored).
-Tig
-
Deleted for duplication of previous message.
-Tig
-
Tigger, that's not correct at all. Ignore whomever gave you this misinformation from now on.
The AIM alliance all have access to the complete PowerPC instruction set. The 162 instructions which AltiVec is comprised of are freely available to all partners. In fact the original engineer who pushed the PowerPC alliance to develop a vector unit was a former Motorola employee working for Apple. There was at no point a restriction made on IBM to produce slow CPUs, that's just 100% rumor bullshit. Motorola doesn't 'own' the instructions, only their implementation which they called AltiVec (which was originally called VMX and after Velocity Engine).
BTW Apple going AMD is another 100% bullshit rumor.
Stop reading rumors, I mean really.
-
@minator,
Even with the new PPC 970 quad-pumped bus architecture AltiVec is still starved for data.
-
strobe wrote:
Tigger, that's not correct at all. Ignore whomever gave you this misinformation from now on.
Ok, so Apple, IBM & Motorola lie in their public statements, and I should trust your source instead??
There was at no point a restriction made on IBM to produce slow CPUs, that's just 100% rumor bullshit. Motorola doesn't 'own' the instructions, only their implementation which they called AltiVec (which was originally called VMX and after Velocity Engine).
Thats completely untrue, IBM can only make G4's to make up shortcomings of Motorola per month, and cannot sell G4 class processors faster or cheaper then Motorola. IBM can sell thier G3's at whatever speed and price they want,but thay cannot sell G4s in the same way. Thats why the 970 is coming out, by reengineering Altivec, they no longer have to follow these rules.
BTW Apple going AMD is another 100% bullshit rumor.
Stop reading rumors, I mean really.
Its a rumor thats going to be mentioned in two major magazines in April, it may not be true, but the Opteron rumor is big enough to be major story come April, so lets not act like I made it up.
-Tig
-
Let's ignore rumors and corporate statements.
Fact is that the G3 have a 133MHz bus, the G4 a 166MHz bus.
-
JetRacer wrote:
Let's ignore rumors and corporate statements.
Fact is that the G3 have a 133MHz bus, the G4 a 166MHz bus.
I think at the 400 Mhz rating I was comparing them at, they have the same bus speed. Again I picked as close as I could to give a real delta. Since Lightwave does not run without Altivec on a G4, I had to do what I did. The 15% delta is pretty small (actually smaller then I thought we'd see), but is for a real world application and repeatable, so its much better info then the guess work we've seen elsewhere on this thread.
-Tig