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Old 04-20-2008, 12:15 PM   #16
johnsfine
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Quote:
Originally Posted by lazlow View Post
When you do see a huge difference in speed is in apps like video conversion (avi->mpg) or anything that would bring a 1ghz PIII to its knees. Then you can see (30%?) differences.
The fact that a problem is slow on a 1ghz PIII is no indication of whether 64bit mode will be faster or slower than 32bit mode on a new CPU.

Many applications are slow on old CPUs primarily because the cache is too small. They'll run much faster on a new CPU because the cache is larger. They'll run slightly faster in 32bit mode than 64bit mode because more 32bit pointers fit in the same size cache.

If an application used 64bit integers, then it could run much faster in 64bit mode than 32bit mode. But I doubt that is likely in video conversion.

Did you measure a 30% difference? Or did you just expect it?

I don't have specific knowledge of avi->mpg conversion, but I think video conversion is the type of application where good use of the XMM registers by the compiler would make a big difference. I don't know what it takes to get GCC in 32bit mode to make good use of XMM registers. Maybe it just can't. My small attempts in that direction have been total failures. I think GCC in 64bit mode does make good use of XMM registers. Some part of the difference may be the fact that 64bit mode has 16 XMM registers, while 32bit mode has only 8. But my best guess is that isn't much of a factor (8 vs. 16 general registers is a very significant difference to GCC. 8 vs. 16 XMM registers should be less so).

I expect the real difference (assuming you are really seeing one) is more an anomaly of GCC development than a fundamental architectural advantage of 64bit mode.

But for the end user, there is no real difference between GCC development effects and fundamental architecture differences. 64bit mode has good reason to be a far more interesting playground for GCC developers. I expect them to do a better job generating good code for 64bit mode than for 32bit mode and I expect that difference to increase over time. So maybe the biggest advantage of 64bit mode will be (or maybe already is) the fact that the GCC developers did a better job of supporting it.
 
Old 04-20-2008, 12:54 PM   #17
lazlow
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When I was referring the the PIII it was just the type of app. Firefox, Thunderbird, etc run fine on a PIII, but video conversions and those "types " of apps that will bring a PIII to its knees are different. Those "types" of apps are the most likely to benefit from 64bit.

Yes, I measured a 30% (roughly) decrease in time needed to change the exact same video from avi->mpg on the same exact hardware. I switched from 32bit F8 to 64bit F8 using Avidemux (same version #, but different package).

As to the why: I really have no idea. I really do not care either. It just is. I suspect that the number who actually care is probably pretty limited. If someone comes up with a definitive answer and tells me, I will say "Oh thats nice". It will matter to me about as much as why the sky is blue, interesting but in the end irrelevant to my daily life.
 
Old 04-20-2008, 01:42 PM   #18
johnsfine
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Quote:
Originally Posted by lazlow View Post
Yes, I measured a 30% (roughly) decrease in time needed to change the exact same video from avi->mpg on the same exact hardware. I switched from 32bit F8 to 64bit F8 using Avidemux (same version #, but different package).
I assume that means you used precompiled binaries in both cases and the 32bit precompiled binaries were compiled for something like generic 486.

I wonder how well 32bit Avidemux would run if compiled for your specific CPU.

I wouldn't actually know how to test that myself. Typically, you download source, then configure, then make. But in that configure step, for a 32bit build, I have no idea how you might tell it you want it compiled for just the local machine rather than for generic 486. As I mentioned earlier, there isn't yet any significant difference between compiling for generic X86_64 and compiling for a specific model of X86_64.

Quote:
As to the why: I really have no idea. I really do not care either. It just is. I suspect that the number who actually care is probably pretty limited.
The reason I though "why" matters in this thread is to know how applicable your experience with Avidemux would be to someone else's expected results with some other application.

"Why" also matters more to me because I'm a software developer working on a product whose execution speed is very important and which is sold with both 32bit and 64bit builds and needs 64bit for some larger problems, but currently runs faster in the Windows 32bit build than either Linux build or the Windows 64bit. That is probably more related to which compiler is available in each environment than to architectural issues (Intel compilers have beaten GCC and MS for this application and Intel 7.1 only available for 32bit Windows has beaten newer Intel versions). But I want to understand and improve things.
 
Old 04-20-2008, 03:29 PM   #19
Sunfist
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Well I might have run into one problem. When I tried to install a flashplayer addon today I got the error message that the software was not compatible with i86_64 linux, not positive, but sounds like it was written for a 32bit Linux and didnt like the fact that I was tring to install it on a 64bit version. What is WinXP anyway, isnt it 64 bit?
 
Old 04-20-2008, 03:34 PM   #20
lazlow
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You use nspluginwrapper as I recall. It is available via most distros package manager.

Most Xp are 32bit but there are 64bit variants.
 
  


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