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PhysX: an easy target ?

with 22 comments

Interesting technical article, called “PhysX: An easy target?“, was posted by user Bohemiq Scali at Window Live blogs.

First part of the entry is dedicated to brief overview of PhysX vs AMD’s physics solutions topic, similar to our “AMD and PhysX: History of the Problem” article, and can be read briefly.

But second part is focused on recent PhysX and x87 theme, and original “PhysX87: Software Deficiency” article by David Kanter. Original statement of mr. Kanter sounds like  “SSE can easily run 1.3-2X faster than similar x87 code“, and that’s where Scali gives him a full pack of criticism:

Kanter then makes claims about the gains that can be had from converting the code to SSE. He claims that SSE could quadruple performance in theory, and in reality a boost of more than 2x would be possible. Kanter claims that a modern optimizing compiler can easily vectorize the code for SSE automatically, and such gains could be had from just a recompile.

So nVidia is just leaving all this performance on the table. What’s more, if PhysX would indeed be 2-4 times faster on CPU, it would actually be a threat to GPU-accelerated physics. Kanter claims that PhysX is hobbled on the CPU, and that nVidia is deliberately doing this to make GPU physics look good.

while, actually, “magic” SSE powers were a little exaggerated, since recent tests (#1; #2) with no-doubt SSE optimized Bullet physics engine have shown that

In synthetic tests, there is about 8% to be gained from recompiling. This is nowhere near the 2-4x figure that Kanter was using. In fact, 8% faster PhysX processing would mean even less than 8% higher framerates in games, since PhysX is not the only CPU-intensive task in a game.

Perhaps the net gain in framerate would be closer to 3-4%, depending on the game. In other words, recompiling PhysX with SSE would not make CPUs threaten GPU physics. Not even close. The difference would be lost in the margin of error, most likely.

but in spite of this

Kanter’s article, wrong as it may be, is linked on many news sites and forums all over the web, and many discussions ensue. Most people buy into Kanter’s article, and some sites make even more bold claims than Kanter himself, referring to Kanter’s article as ‘absolute proof’ of nVidia’s evil actions. This is exactly what AMD needs.

Sum:

You may found Scali’s article biased (AMD conspiracy theory and stuff), but it is worth a read as it has common sense. Give it a glimpse, and share your thoughts.

Also, don’t forget that PhysX SDK 2.8.4 already includes SSE2 compiler option, and should be included into next release of FluidMark, so we’re hoping to perform some tests soon.

Written by Zogrim

September 18th, 2010 at 6:21 pm

Posted in Articles, Reviews, PhysX SDK

Tagged with ,

22 Responses to 'PhysX: an easy target ?'

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  1. Many games are throwing stuff right in your face
    Not many of them requiring GPU acceleration for that artistic stuff.

    But much more realistic than glass just falling through floor, like default one in ME
    Still, i find the price is pretty high – GPU PhysX even consumes up to 33% of performance on single GPU.

    If AMD would have bought PhysX, not Nvidia – same situation would have happen.
    Perhaps. Or perhaps not. I doubt amd/ati would use similar aggressive marketing. Maybe they would even end up with a stand-alone solution similar to Ageia PPUs that would happily work without checking VendorIDs and without blocking features. Also they could optimize it for CPUs (for real) since amd would benefit.
    They simply don’t seem to be that selfish in their past actions, but still i’d like to see what would really happen.

      

    GenL

    21 Sep 10 at 11:45 pm

  2. but still i’d like to see what would really happen
    Me either.
    Cause cavalry (SDK 3.x series and APEX) still haven’t arrived – right now many things on hardware PhysX field are still more like in good (bad, actually) old Ageia times.

      

    Zogrim

    22 Sep 10 at 1:03 am


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