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SIMD in the 90s: Programming Intel's Pentium MMX

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Re: SIMD in the 90s: Programming Intel's Pentium MMX

#31

Post by jamesu »

ColdStream wrote: post #24

When MMX first came out and there were games that supported it, many reviewers were convinced that it improved 3D performance. As far as I could tell, it wasn't really used for 3D and that the only enhancement was to the audio system. But the placebo effect of "If has MMX thus its better" did stick around for a long while. An aside, but when SSE came a long that was a real big leap in 3D performance, just as GPU's st…

AFAIK, MMX was more for fixed point math (as also pointed out by another commenter) which would explain why it wasn't used much for 3D. You tended to see it more in image and sound processing code. Maybe the reviewers got it mixed up with 3DNow.

Re: SIMD in the 90s: Programming Intel's Pentium MMX

#32

Post by ack_complete »

jamesu wrote: post #31
ColdStream wrote: post #24

When MMX first came out and there were games that supported it, many reviewers were convinced that it improved 3D performance. As far as I could tell, it wasn't really used for 3D and that the only enhancement was to the audio system. But the placebo effect of "If has MMX thus its better" did stick around for a long while. An aside, but when SSE came a long that was a real big leap in 3D performance, just as GPU's st…

AFAIK, MMX was more for fixed point math (as also pointed out by another commenter) which would explain why it wasn't used much for 3D. You tended to see it more in image and sound processing code. Maybe the reviewers got it mixed up with 3DNow.

MMX did help significantly with software 3D rendering. I worked on a software rasterizer that benefited significantly from it. But it didn't take long before even a well-optimized software renderer on a high end CPU couldn't keep up with a low end GPU on a low end CPU.

Re: SIMD in the 90s: Programming Intel's Pentium MMX

#33

Post by zir_blazer »

ack_complete wrote: post #12
zir_blazer wrote: post #10

Earlier quoted context omitted.

> Additionally, some CPUs at the time only had a 64-bit data path and had to split SSE2 ops, but because of their 4-1-1 decode template, could only decode one such instruction per cycle. I believe that only the first Pentium 3 core, Katmai, did this. > This caused some confusion with the 64-bit version of Windows since Microsoft tried to say that x87/MMX shouldn't be used in long mode, but after queries from video pr…

> I believe that only the first Pentium 3 core, Katmai, did this. No, all Pentium 3s as well as the Pentium M. Pentium 4 notably didn't suffer from it, but it of course had many, many, MANY other performance issues. > I have some faint memories of hearing somewhere that Long Mode didn't support x87. I wonder if it is related to this early info you mention and it being Microsoft specific. It was VM86 mode that Long Mo…

>> I believe that only the first Pentium 3 core, Katmai, did this.

> No, all Pentium 3s as well as the Pentium M. Pentium 4 notably didn't suffer from it, but it of course had many, many, MANY other performance issues.

I had to google a bit to confirm this, and seems like I'm not the only one that understood it the way I did:

https://www.vogons.org/viewtopic.php?p=1360606#p1360606

https://www.vogons.org/viewtopic.php?p=1360620#p1360620

Basically, the info I knew was that Katmai had 128 Bits SSE registers but processed it as 2x64 Bits. That info is well reference pretty much everywhere. What is NOT explicitly mentioned is whenever Coppermine/Tualatin maintained that arrangement or had 128 Bits compute units for SSE, so the wording always made Katmai to look like an exception, as if everything else was 128 Bits.

Re: SIMD in the 90s: Programming Intel's Pentium MMX

#34

Post by justsomehnguy »

monocasa wrote: post #27
justsomehnguy wrote: post #20

Earlier quoted context omitted.

Well, GPUs in a modern understanding didn't came till GF4/GF4MX, when you could get something for less than $50.. at this moment MMX wasn't anywhere because SSE was. At this point you had an overlay display for the DivX/XviD and your average CPU could display the realtime video.

It came from GF3, which had full vertex and pixel shaders. Also, the GF4MX was just a GeForce256 in a trenchcoat, and didn't have vertex shaders (at least exposed to software, the T&L engine was still a vertex shader like engine, only the code was all written by nvidia and loaded from ROM).

Well yes but no.

GF3 was a very short lived product, even more short lived than GF2MX.

And the crucial thing here is what at the time of GF/GF2 you still could buy a computer without a proper[0] 3D and video output acceleration[1], but by the time of GF4MX (which is GF2MX on the booster shoes and VPE - and only a year and half later at the worst) you have no option not to get a full package.

SIS died, 3Dfx died even earlier, S3 became irrelevant and Intel was for the button pushers till i945 - which came only in 2005.

And while at first the price even for GF4MX420 was ~$100 it did two things:

- pushed the price for GF2MX series well below $50 (and quite soon followed the suit) so anything now had DX7 level 3D on-board

- pushed the price for every other 3D accelerator waaay down

- made MPEG and video acceleration the default in everything

[0] emphasis on the 'proper'

[1] though you needed to get out of the way to do so, eg i815, G450 - but you could!

Re: SIMD in the 90s: Programming Intel's Pentium MMX

#35

Post by pseudohadamard »

Go to page. Nothing. Enable Javascript for it. Still nothing. Enable more Javascript. Still nothing. Third lot of Javascript and now it finally renders.

It's static text with a few images... that doesn't display until you tell NoScript to enable Javascript from a pile of third-party sites.

Re: SIMD in the 90s: Programming Intel's Pentium MMX

#36

Post by moosedev »

Nition wrote: post #14
theandrewbailey wrote: post #9

> Each MMX register is 64 bits wide. Internally, the MMX registers were aliases of the x87 floating-point registers. Due to the way the first Pentium 3 CPUs (Katmai) were built, they likewise aliased the x87 (and thus, MMX) registers to the XMM SSE registers, but this was hidden from programs. It wasn't until at least the Coppermine revision that they were separate registers again.

I remember hearing a rumour as a young teen that the Coppermine codename meant it actually had copper wiring and that's what made it faster somehow. Copper has lower resistance than aluminium and can therefore help chips run faster - it makes sense! But it was just a codename and the coppermine had aluminium interconnects. My family got a PIII 533Mhz coppermine, in the early sideways Slot 1 configuration. Blazing fas…

(Code)named after https://en.wikipedia.org/wiki/Coppermine_River , apparently.

POD was pretty rad :) Thanks for the reminder of it (and all the MMX marketing around it.)

Re: SIMD in the 90s: Programming Intel's Pentium MMX

#37

Post by kristianp »

Enjoying the "DOS" font of the code examples.

The wikipedia page on the Pentium has multiple references to an Intel publication called "Solutions", May/June 1993. It would be interesting to see that, but can't find a copy.

https://en.wikipedia.org/wiki/Pentium_(original)#cite_note-1...

Re: SIMD in the 90s: Programming Intel's Pentium MMX

#38

Post by LoganDark »

kristianp wrote: post #37

Enjoying the "DOS" font of the code examples. The wikipedia page on the Pentium has multiple references to an Intel publication called "Solutions", May/June 1993. It would be interesting to see that, but can't find a copy. https://en.wikipedia.org/wiki/Pentium_(original)#cite_note-1...

https://int10h.org/oldschool-pc-fonts/readme/

Re: SIMD in the 90s: Programming Intel's Pentium MMX

#39

Post by 245425456g »

theandrewbailey wrote: post #9

> Each MMX register is 64 bits wide. Internally, the MMX registers were aliases of the x87 floating-point registers. Due to the way the first Pentium 3 CPUs (Katmai) were built, they likewise aliased the x87 (and thus, MMX) registers to the XMM SSE registers, but this was hidden from programs. It wasn't until at least the Coppermine revision that they were separate registers again.

No, x87/MMX and SSE XMM were not aliased. They were two separate register files.

(You may be confusing it with XMM vs YMM vs ZMM, i.e. SSE vs AVX vs AVX512.)

Re: SIMD in the 90s: Programming Intel's Pentium MMX

#40

Post by 245425456g »

Nition wrote: post #14
theandrewbailey wrote: post #9

> Each MMX register is 64 bits wide. Internally, the MMX registers were aliases of the x87 floating-point registers. Due to the way the first Pentium 3 CPUs (Katmai) were built, they likewise aliased the x87 (and thus, MMX) registers to the XMM SSE registers, but this was hidden from programs. It wasn't until at least the Coppermine revision that they were separate registers again.

I remember hearing a rumour as a young teen that the Coppermine codename meant it actually had copper wiring and that's what made it faster somehow. Copper has lower resistance than aluminium and can therefore help chips run faster - it makes sense! But it was just a codename and the coppermine had aluminium interconnects. My family got a PIII 533Mhz coppermine, in the early sideways Slot 1 configuration. Blazing fas…

P3 Coppermine was 0.18 µm. P3 Tualatin was 0.13 µm with Cu and low-K.

So no, Coppermine had nothing to do with Cu in the process.

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